Make it possible to include llvm-c without including C++ headers. Patch by Filip Pizlo.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178713 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/llvm-c/ExecutionEngine.h b/include/llvm-c/ExecutionEngine.h
index cb77bb2..6ca316c 100644
--- a/include/llvm-c/ExecutionEngine.h
+++ b/include/llvm-c/ExecutionEngine.h
@@ -138,7 +138,9 @@
 
 #ifdef __cplusplus
 }
+#endif
 
+#if defined(__cplusplus) && !defined(LLVM_DO_NOT_INCLUDE_CPP_HEADERS)
 namespace llvm {
   struct GenericValue;
   class ExecutionEngine;
@@ -157,7 +159,6 @@
   
   #undef DEFINE_SIMPLE_CONVERSION_FUNCTIONS
 }
-  
-#endif /* defined(__cplusplus) */
+#endif /* defined(__cplusplus) && !defined(LLVM_DO_NOT_INCLUDE_CPP_HEADERS) */
 
 #endif