Ignore -Wgcc-compat diagnostic in StringLiteral.

llvm-svn: 289856

llvm/include/llvm/ADT/StringRef.h

@@ -847,9 +847,12 @@ namespace llvm {
   public:
     template <size_t N>
     constexpr StringLiteral(const char (&Str)[N])
-#if __has_attribute(enable_if)
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wgcc-compat"
         __attribute((enable_if(__builtin_strlen(Str) == N - 1,
                                "invalid string literal")))
+#pragma clang diagnostic pop
 #endif
         : StringRef(Str, N - 1) {
     }