Fix C++03 build

llvm-svn: 288555
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 5877920183809117560cded151e054f720fcee18
diff --git a/include/variant b/include/variant
index 45efc78..94c1ece 100644
--- a/include/variant
+++ b/include/variant
@@ -216,7 +216,7 @@
 
 class _LIBCPP_EXCEPTION_ABI bad_variant_access : public exception {
 public:
-  _LIBCPP_FUNC_VIS virtual const char* what() const noexcept;
+  _LIBCPP_FUNC_VIS virtual const char* what() const _NOEXCEPT;
 };
 
 } // namespace std