Don't define these unless we plan to use them.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145289 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/Valgrind.cpp

@@ -53,6 +53,7 @@ void llvm::sys::ValgrindDiscardTranslations(const void *Addr, size_t Len) {
 
 #endif  // !HAVE_VALGRIND_VALGRIND_H
 
+#if LLVM_ENABLE_THREADS != 0 && !defined(NDEBUG)
 // These functions require no implementation, tsan just looks at the arguments
 // they're called with.
 extern "C" {
@@ -63,3 +64,4 @@ void AnnotateHappensAfter(const char *file, int line,
 void AnnotateIgnoreWritesBegin(const char *file, int line) {}
 void AnnotateIgnoreWritesEnd(const char *file, int line) {}
 }
+#endif