Wrap C APIs with pragmas enforcing -Werror=strict-prototypes

Force `-Werror=strict-prototypes` so that C API tests fail to compile if
we add a non-prototype declaration.  This should help avoid regressions
like bddecba4b333f7772029b4937d2c34f9f2fda6ca was fixing.

https://reviews.llvm.org/D70285
rdar://problem/57203137
diff --git a/llvm/include/llvm-c/Analysis.h b/llvm/include/llvm-c/Analysis.h
index cb9e8ec..270b145 100644
--- a/llvm/include/llvm-c/Analysis.h
+++ b/llvm/include/llvm-c/Analysis.h
@@ -19,11 +19,10 @@
 #ifndef LLVM_C_ANALYSIS_H
 #define LLVM_C_ANALYSIS_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCAnalysis Analysis
@@ -58,8 +57,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/BitReader.h b/llvm/include/llvm-c/BitReader.h
index b307ee9..012c0e6 100644
--- a/llvm/include/llvm-c/BitReader.h
+++ b/llvm/include/llvm-c/BitReader.h
@@ -19,11 +19,10 @@
 #ifndef LLVM_C_BITREADER_H
 #define LLVM_C_BITREADER_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCBitReader Bit Reader
@@ -78,8 +77,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/BitWriter.h b/llvm/include/llvm-c/BitWriter.h
index 1870515..ea84b65 100644
--- a/llvm/include/llvm-c/BitWriter.h
+++ b/llvm/include/llvm-c/BitWriter.h
@@ -19,11 +19,10 @@
 #ifndef LLVM_C_BITWRITER_H
 #define LLVM_C_BITWRITER_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCBitWriter Bit Writer
@@ -52,8 +51,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Comdat.h b/llvm/include/llvm-c/Comdat.h
index 81fee3f..45b4007 100644
--- a/llvm/include/llvm-c/Comdat.h
+++ b/llvm/include/llvm-c/Comdat.h
@@ -14,11 +14,10 @@
 #ifndef LLVM_C_COMDAT_H
 #define LLVM_C_COMDAT_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 typedef enum {
   LLVMAnyComdatSelectionKind,        ///< The linker may choose any COMDAT.
@@ -68,8 +67,6 @@
  */
 void LLVMSetComdatSelectionKind(LLVMComdatRef C, LLVMComdatSelectionKind Kind);
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Core.h b/llvm/include/llvm-c/Core.h
index 83bf707..7a39731 100644
--- a/llvm/include/llvm-c/Core.h
+++ b/llvm/include/llvm-c/Core.h
@@ -16,11 +16,10 @@
 #define LLVM_C_CORE_H
 
 #include "llvm-c/ErrorHandling.h"
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMC LLVM-C: C interface to LLVM
@@ -4090,8 +4089,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif /* LLVM_C_CORE_H */
diff --git a/llvm/include/llvm-c/DebugInfo.h b/llvm/include/llvm-c/DebugInfo.h
index 41e9f96b..ab60b88 100644
--- a/llvm/include/llvm-c/DebugInfo.h
+++ b/llvm/include/llvm-c/DebugInfo.h
@@ -17,10 +17,9 @@
 #define LLVM_C_DEBUGINFO_H
 
 #include "llvm-c/Core.h"
+#include "llvm-c/ExternC.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * Debug info flags.
@@ -1353,8 +1352,6 @@
  */
 LLVMMetadataKind LLVMGetMetadataKind(LLVMMetadataRef Metadata);
 
-#ifdef __cplusplus
-} /* end extern "C" */
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Disassembler.h b/llvm/include/llvm-c/Disassembler.h
index 3adcc3c..b1cb35d 100644
--- a/llvm/include/llvm-c/Disassembler.h
+++ b/llvm/include/llvm-c/Disassembler.h
@@ -16,6 +16,7 @@
 #define LLVM_C_DISASSEMBLER_H
 
 #include "llvm-c/DisassemblerTypes.h"
+#include "llvm-c/ExternC.h"
 
 /**
  * @defgroup LLVMCDisassembler Disassembler
@@ -24,9 +25,7 @@
  * @{
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif /* !defined(__cplusplus) */
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * Create a disassembler for the TripleName.  Symbolic disassembly is supported
@@ -106,8 +105,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* !defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif /* LLVM_C_DISASSEMBLER_H */
diff --git a/llvm/include/llvm-c/Error.h b/llvm/include/llvm-c/Error.h
index 5294306..92f81bf 100644
--- a/llvm/include/llvm-c/Error.h
+++ b/llvm/include/llvm-c/Error.h
@@ -14,9 +14,9 @@
 #ifndef LLVM_C_ERROR_H
 #define LLVM_C_ERROR_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+#include "llvm-c/ExternC.h"
+
+LLVM_C_EXTERN_C_BEGIN
 
 #define LLVMErrorSuccess 0
 
@@ -62,8 +62,6 @@
  */
 LLVMErrorTypeId LLVMGetStringErrorTypeId(void);
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/ErrorHandling.h b/llvm/include/llvm-c/ErrorHandling.h
index 4927349..c6f7ff3 100644
--- a/llvm/include/llvm-c/ErrorHandling.h
+++ b/llvm/include/llvm-c/ErrorHandling.h
@@ -14,9 +14,9 @@
 #ifndef LLVM_C_ERROR_HANDLING_H
 #define LLVM_C_ERROR_HANDLING_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+#include "llvm-c/ExternC.h"
+
+LLVM_C_EXTERN_C_BEGIN
 
 typedef void (*LLVMFatalErrorHandler)(const char *Reason);
 
@@ -42,8 +42,6 @@
  */
 void LLVMEnablePrettyStackTrace(void);
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/ExecutionEngine.h b/llvm/include/llvm-c/ExecutionEngine.h
index ef714cd..f31b97a 100644
--- a/llvm/include/llvm-c/ExecutionEngine.h
+++ b/llvm/include/llvm-c/ExecutionEngine.h
@@ -19,13 +19,12 @@
 #ifndef LLVM_C_EXECUTIONENGINE_H
 #define LLVM_C_EXECUTIONENGINE_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Target.h"
 #include "llvm-c/TargetMachine.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCExecutionEngine Execution Engine
@@ -193,8 +192,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/ExternC.h b/llvm/include/llvm-c/ExternC.h
new file mode 100644
index 0000000..4240f7c
--- /dev/null
+++ b/llvm/include/llvm-c/ExternC.h
@@ -0,0 +1,39 @@
+/*===- llvm-c/ExternC.h - Wrapper for 'extern "C"' ----------------*- C -*-===*\
+|*                                                                            *|
+|* Part of the LLVM Project, under the Apache License v2.0 with LLVM          *|
+|* Exceptions.                                                                *|
+|* See https://llvm.org/LICENSE.txt for license information.                  *|
+|* SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception                    *|
+|*                                                                            *|
+|*===----------------------------------------------------------------------===*|
+|*                                                                            *|
+|* This file defines an 'extern "C"' wrapper                                  *|
+|*                                                                            *|
+\*===----------------------------------------------------------------------===*/
+
+#ifndef LLVM_C_EXTERN_C_H
+#define LLVM_C_EXTERN_C_H
+
+#ifdef __clang__
+#define LLVM_C_STRICT_PROTOTYPES_BEGIN                                         \
+  _Pragma("clang diagnostic push")                                             \
+      _Pragma("clang diagnostic error \"-Wstrict-prototypes\"")
+#define LLVM_C_STRICT_PROTOTYPES_END _Pragma("clang diagnostic pop")
+#else
+#define LLVM_C_STRICT_PROTOTYPES_BEGIN
+#define LLVM_C_STRICT_PROTOTYPES_END
+#endif
+
+#ifdef __cplusplus
+#define LLVM_C_EXTERN_C_BEGIN                                                  \
+  extern "C" {                                                                 \
+  LLVM_C_STRICT_PROTOTYPES_BEGIN
+#define LLVM_C_EXTERN_C_END                                                    \
+  LLVM_C_STRICT_PROTOTYPES_END                                                 \
+  }
+#else
+#define LLVM_C_EXTERN_C_BEGIN LLVM_C_STRICT_PROTOTYPES_BEGIN
+#define LLVM_C_EXTERN_C_END LLVM_C_STRICT_PROTOTYPES_END
+#endif
+
+#endif
diff --git a/llvm/include/llvm-c/IRReader.h b/llvm/include/llvm-c/IRReader.h
index 4d0b696..5a3f633 100644
--- a/llvm/include/llvm-c/IRReader.h
+++ b/llvm/include/llvm-c/IRReader.h
@@ -14,11 +14,10 @@
 #ifndef LLVM_C_IRREADER_H
 #define LLVM_C_IRREADER_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * Read LLVM IR from a memory buffer and convert it into an in-memory Module
@@ -33,8 +32,6 @@
                               LLVMMemoryBufferRef MemBuf, LLVMModuleRef *OutM,
                               char **OutMessage);
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Initialization.h b/llvm/include/llvm-c/Initialization.h
index 36c41db..0d59de8 100644
--- a/llvm/include/llvm-c/Initialization.h
+++ b/llvm/include/llvm-c/Initialization.h
@@ -16,11 +16,10 @@
 #ifndef LLVM_C_INITIALIZATION_H
 #define LLVM_C_INITIALIZATION_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCInitialization Initialization Routines
@@ -49,8 +48,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/LinkTimeOptimizer.h b/llvm/include/llvm-c/LinkTimeOptimizer.h
index 19b4f5c..9ae65b8 100644
--- a/llvm/include/llvm-c/LinkTimeOptimizer.h
+++ b/llvm/include/llvm-c/LinkTimeOptimizer.h
@@ -15,9 +15,9 @@
 #ifndef LLVM_C_LINKTIMEOPTIMIZER_H
 #define LLVM_C_LINKTIMEOPTIMIZER_H
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+#include "llvm-c/ExternC.h"
+
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCLinkTimeOptimizer Link Time Optimization
@@ -61,8 +61,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+  LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Linker.h b/llvm/include/llvm-c/Linker.h
index 9085130..1ad9cc9 100644
--- a/llvm/include/llvm-c/Linker.h
+++ b/llvm/include/llvm-c/Linker.h
@@ -14,11 +14,10 @@
 #ifndef LLVM_C_LINKER_H
 #define LLVM_C_LINKER_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /* This enum is provided for backwards-compatibility only. It has no effect. */
 typedef enum {
@@ -34,8 +33,6 @@
 */
 LLVMBool LLVMLinkModules2(LLVMModuleRef Dest, LLVMModuleRef Src);
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Object.h b/llvm/include/llvm-c/Object.h
index 1e9b703..9a9596a 100644
--- a/llvm/include/llvm-c/Object.h
+++ b/llvm/include/llvm-c/Object.h
@@ -19,12 +19,11 @@
 #ifndef LLVM_C_OBJECT_H
 #define LLVM_C_OBJECT_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 #include "llvm/Config/llvm-config.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCObject Object file reading and writing
@@ -226,8 +225,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/OrcBindings.h b/llvm/include/llvm-c/OrcBindings.h
index 9e92371..11cdade 100644
--- a/llvm/include/llvm-c/OrcBindings.h
+++ b/llvm/include/llvm-c/OrcBindings.h
@@ -23,12 +23,11 @@
 #define LLVM_C_ORCBINDINGS_H
 
 #include "llvm-c/Error.h"
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Object.h"
 #include "llvm-c/TargetMachine.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 typedef struct LLVMOrcOpaqueJITStack *LLVMOrcJITStackRef;
 typedef uint64_t LLVMOrcModuleHandle;
@@ -165,8 +164,6 @@
  */
 void LLVMOrcUnregisterJITEventListener(LLVMOrcJITStackRef JITStack, LLVMJITEventListenerRef L);
 
-#ifdef __cplusplus
-}
-#endif /* extern "C" */
+LLVM_C_EXTERN_C_END
 
 #endif /* LLVM_C_ORCBINDINGS_H */
diff --git a/llvm/include/llvm-c/Remarks.h b/llvm/include/llvm-c/Remarks.h
index 5444aeb..ffe647a 100644
--- a/llvm/include/llvm-c/Remarks.h
+++ b/llvm/include/llvm-c/Remarks.h
@@ -15,14 +15,16 @@
 #ifndef LLVM_C_REMARKS_H
 #define LLVM_C_REMARKS_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 #ifdef __cplusplus
 #include <cstddef>
-extern "C" {
 #else
 #include <stddef.h>
 #endif /* !defined(__cplusplus) */
 
+LLVM_C_EXTERN_C_BEGIN
+
 /**
  * @defgroup LLVMCREMARKS Remarks
  * @ingroup LLVMC
@@ -337,8 +339,6 @@
  * @} // endgoup LLVMCREMARKS
  */
 
-#ifdef __cplusplus
-}
-#endif /* !defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif /* LLVM_C_REMARKS_H */
diff --git a/llvm/include/llvm-c/Support.h b/llvm/include/llvm-c/Support.h
index 097f784..866df32 100644
--- a/llvm/include/llvm-c/Support.h
+++ b/llvm/include/llvm-c/Support.h
@@ -15,11 +15,10 @@
 #define LLVM_C_SUPPORT_H
 
 #include "llvm-c/DataTypes.h"
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * This function permanently loads the dynamic library at the given path.
@@ -58,8 +57,6 @@
  */
 void LLVMAddSymbol(const char *symbolName, void *symbolValue);
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Target.h b/llvm/include/llvm-c/Target.h
index 4ef641e..518b46d 100644
--- a/llvm/include/llvm-c/Target.h
+++ b/llvm/include/llvm-c/Target.h
@@ -19,12 +19,11 @@
 #ifndef LLVM_C_TARGET_H
 #define LLVM_C_TARGET_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 #include "llvm/Config/llvm-config.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCTarget Target information
@@ -288,8 +287,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/TargetMachine.h b/llvm/include/llvm-c/TargetMachine.h
index 28d7c09..f82edd9 100644
--- a/llvm/include/llvm-c/TargetMachine.h
+++ b/llvm/include/llvm-c/TargetMachine.h
@@ -19,12 +19,12 @@
 #ifndef LLVM_C_TARGETMACHINE_H
 #define LLVM_C_TARGETMACHINE_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Target.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
+
 typedef struct LLVMOpaqueTargetMachine *LLVMTargetMachineRef;
 typedef struct LLVMTarget *LLVMTargetRef;
 
@@ -156,8 +156,6 @@
 /** Adds the target-specific analysis passes to the pass manager. */
 void LLVMAddAnalysisPasses(LLVMTargetMachineRef T, LLVMPassManagerRef PM);
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Transforms/AggressiveInstCombine.h b/llvm/include/llvm-c/Transforms/AggressiveInstCombine.h
index c0b0141..db061a7a 100644
--- a/llvm/include/llvm-c/Transforms/AggressiveInstCombine.h
+++ b/llvm/include/llvm-c/Transforms/AggressiveInstCombine.h
@@ -15,11 +15,10 @@
 #ifndef LLVM_C_TRANSFORMS_AGGRESSIVEINSTCOMBINE_H
 #define LLVM_C_TRANSFORMS_AGGRESSIVEINSTCOMBINE_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCTransformsAggressiveInstCombine Aggressive Instruction Combining transformations
@@ -35,9 +34,7 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
 
diff --git a/llvm/include/llvm-c/Transforms/Coroutines.h b/llvm/include/llvm-c/Transforms/Coroutines.h
index 227e7cf..687f9b5 100644
--- a/llvm/include/llvm-c/Transforms/Coroutines.h
+++ b/llvm/include/llvm-c/Transforms/Coroutines.h
@@ -19,11 +19,10 @@
 #ifndef LLVM_C_TRANSFORMS_COROUTINES_H
 #define LLVM_C_TRANSFORMS_COROUTINES_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCTransformsCoroutines Coroutine transformations
@@ -48,8 +47,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Transforms/IPO.h b/llvm/include/llvm-c/Transforms/IPO.h
index 51d0075..cde3d24 100644
--- a/llvm/include/llvm-c/Transforms/IPO.h
+++ b/llvm/include/llvm-c/Transforms/IPO.h
@@ -15,11 +15,10 @@
 #ifndef LLVM_C_TRANSFORMS_IPO_H
 #define LLVM_C_TRANSFORMS_IPO_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCTransformsIPO Interprocedural transformations
@@ -95,8 +94,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Transforms/InstCombine.h b/llvm/include/llvm-c/Transforms/InstCombine.h
index 166f278..ebe17d6 100644
--- a/llvm/include/llvm-c/Transforms/InstCombine.h
+++ b/llvm/include/llvm-c/Transforms/InstCombine.h
@@ -15,11 +15,10 @@
 #ifndef LLVM_C_TRANSFORMS_INSTCOMBINE_H
 #define LLVM_C_TRANSFORMS_INSTCOMBINE_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCTransformsInstCombine Instruction Combining transformations
@@ -35,9 +34,7 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
 
diff --git a/llvm/include/llvm-c/Transforms/PassManagerBuilder.h b/llvm/include/llvm-c/Transforms/PassManagerBuilder.h
index d164c00..6e13e18 100644
--- a/llvm/include/llvm-c/Transforms/PassManagerBuilder.h
+++ b/llvm/include/llvm-c/Transforms/PassManagerBuilder.h
@@ -14,13 +14,12 @@
 #ifndef LLVM_C_TRANSFORMS_PASSMANAGERBUILDER_H
 #define LLVM_C_TRANSFORMS_PASSMANAGERBUILDER_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
 typedef struct LLVMOpaquePassManagerBuilder *LLVMPassManagerBuilderRef;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCTransformsPassManagerBuilder Pass manager builder
@@ -83,8 +82,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Transforms/Scalar.h b/llvm/include/llvm-c/Transforms/Scalar.h
index 6f3a3d8..93d79a2 100644
--- a/llvm/include/llvm-c/Transforms/Scalar.h
+++ b/llvm/include/llvm-c/Transforms/Scalar.h
@@ -19,11 +19,10 @@
 #ifndef LLVM_C_TRANSFORMS_SCALAR_H
 #define LLVM_C_TRANSFORMS_SCALAR_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCTransformsScalar Scalar transformations
@@ -166,8 +165,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Transforms/Utils.h b/llvm/include/llvm-c/Transforms/Utils.h
index 63594ab..30d1ae6 100644
--- a/llvm/include/llvm-c/Transforms/Utils.h
+++ b/llvm/include/llvm-c/Transforms/Utils.h
@@ -19,11 +19,10 @@
 #ifndef LLVM_C_TRANSFORMS_UTILS_H
 #define LLVM_C_TRANSFORMS_UTILS_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCTransformsUtils Transformation Utilities
@@ -45,9 +44,7 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
 
diff --git a/llvm/include/llvm-c/Transforms/Vectorize.h b/llvm/include/llvm-c/Transforms/Vectorize.h
index e383481..0de4583 100644
--- a/llvm/include/llvm-c/Transforms/Vectorize.h
+++ b/llvm/include/llvm-c/Transforms/Vectorize.h
@@ -20,11 +20,10 @@
 #ifndef LLVM_C_TRANSFORMS_VECTORIZE_H
 #define LLVM_C_TRANSFORMS_VECTORIZE_H
 
+#include "llvm-c/ExternC.h"
 #include "llvm-c/Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCTransformsVectorize Vectorization transformations
@@ -43,8 +42,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif /* defined(__cplusplus) */
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/Types.h b/llvm/include/llvm-c/Types.h
index 612c7d3..4e02498 100644
--- a/llvm/include/llvm-c/Types.h
+++ b/llvm/include/llvm-c/Types.h
@@ -15,10 +15,9 @@
 #define LLVM_C_TYPES_H
 
 #include "llvm-c/DataTypes.h"
+#include "llvm-c/ExternC.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCSupportTypes Types and Enumerations
@@ -172,8 +171,6 @@
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif
diff --git a/llvm/include/llvm-c/lto.h b/llvm/include/llvm-c/lto.h
index 41e6067..0c6ce67 100644
--- a/llvm/include/llvm-c/lto.h
+++ b/llvm/include/llvm-c/lto.h
@@ -16,6 +16,8 @@
 #ifndef LLVM_C_LTO_H
 #define LLVM_C_LTO_H
 
+#include "llvm-c/ExternC.h"
+
 #ifdef __cplusplus
 #include <cstddef>
 #else
@@ -98,9 +100,7 @@
 /** opaque reference to a thin code generator */
 typedef struct LLVMOpaqueThinLTOCodeGenerator *thinlto_code_gen_t;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * Returns a printable string.
@@ -900,8 +900,6 @@
  * @} // endgroup LLVMCTLTO_CACHING
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif /* LLVM_C_LTO_H */