Index: include/llvm/Support/Threading.h
===================================================================
--- include/llvm/Support/Threading.h
+++ include/llvm/Support/Threading.h
@@ -62,7 +62,7 @@
 
   /// This macro is the only way you should define your once flag for LLVM's
   /// call_once.
-#define LLVM_DEFINE_ONCE_FLAG(flag) static once_flag flag
+#define LLVM_DEFINE_ONCE_FLAG(flag) static ::llvm::once_flag flag
 
 #else