Add a libLTO API to stop/restart ThinLTO between optimizations and CodeGen

This allows the linker to instruct ThinLTO to perform only the
optimization part or only the codegen part of the process.

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 265113
diff --git a/llvm/include/llvm-c/lto.h b/llvm/include/llvm-c/lto.h
index 42c2802..82f7fd7 100644
--- a/llvm/include/llvm-c/lto.h
+++ b/llvm/include/llvm-c/lto.h
@@ -44,7 +44,8 @@
  * @{
  */
 
-#define LTO_API_VERSION 18
+#define LTO_API_VERSION 19
+
 /**
  * \since prior to LTO_API_VERSION=3
  */
@@ -718,6 +719,23 @@
 extern void thinlto_codegen_set_cpu(thinlto_code_gen_t cg, const char *cpu);
 
 /**
+ * Disable CodeGen, only run the stages till codegen and stop. The output will
+ * be bitcode.
+ *
+ * \since LTO_API_VERSION=19
+ */
+extern void thinlto_codegen_disable_codegen(thinlto_code_gen_t cg,
+                                            lto_bool_t disable);
+
+/**
+ * Perform CodeGen only: disable all other stages.
+ *
+ * \since LTO_API_VERSION=19
+ */
+extern void thinlto_codegen_set_codegen_only(thinlto_code_gen_t cg,
+                                             lto_bool_t codegen_only);
+
+/**
  * Parse -mllvm style debug options.
  *
  * \since LTO_API_VERSION=18