Patch from Albert J. Wong to make type_traits take advantage of gcc intrinsics in 4.7 and later. No functionality change when using clang.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@211755 91177308-0d34-0410-b5e6-96231b3b80d8

include/__config

@@ -339,7 +339,11 @@ typedef __char32_t char32_t;
 #endif
 
 #if __has_feature(underlying_type)
-#  define _LIBCXX_UNDERLYING_TYPE(T) __underlying_type(T)
+#  define _LIBCPP_UNDERLYING_TYPE(T) __underlying_type(T)
+#endif
+
+#if __has_feature(is_literal)
+#  define _LIBCPP_IS_LITERAL(T) __is_literal(T)
 #endif
 
 // Inline namespaces are available in Clang regardless of C++ dialect.
@@ -363,6 +367,11 @@ namespace std {
 
 #define _LIBCPP_NORETURN __attribute__((noreturn))
 
+#if _GNUC_VER >= 407
+#define _LIBCPP_UNDERLYING_TYPE(T) __underlying_type(T)
+#define _LIBCPP_IS_LITERAL(T) __is_literal_type(T)
+#endif
+
 #if !__EXCEPTIONS
 #define _LIBCPP_NO_EXCEPTIONS
 #endif