Implement __underlying_type for libc++.

llvm-svn: 131633
diff --git a/clang/lib/Parse/ParseTentative.cpp b/clang/lib/Parse/ParseTentative.cpp
index 12152c3..78d2c90 100644
--- a/clang/lib/Parse/ParseTentative.cpp
+++ b/clang/lib/Parse/ParseTentative.cpp
@@ -694,6 +694,7 @@
   case tok::kw_char16_t:
   case tok::kw_char32_t:
   case tok::kw_decltype:
+  case tok::kw___underlying_type:
   case tok::kw_thread_local:
   case tok::kw__Decimal32:
   case tok::kw__Decimal64:
@@ -1012,6 +1013,10 @@
   case tok::kw_decltype:
     return TPResult::True();
 
+  // C++0x type traits support
+  case tok::kw___underlying_type:
+    return TPResult::True();
+
   default:
     return TPResult::False();
   }