Index: include/llvm/Support/Threading.h
===================================================================
--- include/llvm/Support/Threading.h
+++ include/llvm/Support/Threading.h
@@ -71,7 +71,8 @@
 
   /// 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 = Uninitialized
+#define LLVM_DEFINE_ONCE_FLAG(flag) \
+  static llvm::once_flag flag = llvm::Uninitialized
 
 #endif