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

llvm-svn: 145289
diff --git a/llvm/lib/Support/Valgrind.cpp b/llvm/lib/Support/Valgrind.cpp
index 078d705..2b250a3 100644
--- a/llvm/lib/Support/Valgrind.cpp
+++ b/llvm/lib/Support/Valgrind.cpp
@@ -53,6 +53,7 @@
 
 #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 AnnotateIgnoreWritesBegin(const char *file, int line) {}
 void AnnotateIgnoreWritesEnd(const char *file, int line) {}
 }
+#endif