Update llvm-c headers for Version 11.0.1

src/llvm-c/BitWriter.h

@@ -19,11 +19,10 @@
 #ifndef LLVM_C_BITWRITER_H
 #define LLVM_C_BITWRITER_H
 
+#include "ExternC.h"
 #include "Types.h"
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+LLVM_C_EXTERN_C_BEGIN
 
 /**
  * @defgroup LLVMCBitWriter Bit Writer
@@ -52,8 +51,6 @@ LLVMMemoryBufferRef LLVMWriteBitcodeToMemoryBuffer(LLVMModuleRef M);
  * @}
  */
 
-#ifdef __cplusplus
-}
-#endif
+LLVM_C_EXTERN_C_END
 
 #endif