In stdbool.h, define bool, false, true only in gnu++98

GCC has meanwhile corrected that with the similar
<https://gcc.gnu.org/viewcvs/gcc?view=revision&revision=216679> "C++11
explicitly forbids macros for bool, true and false."

Differential Revision: https://reviews.llvm.org/D40167

llvm-svn: 320135
diff --git a/clang/lib/Headers/stdbool.h b/clang/lib/Headers/stdbool.h
index 0467893..5cb66b5 100644
--- a/clang/lib/Headers/stdbool.h
+++ b/clang/lib/Headers/stdbool.h
@@ -32,12 +32,15 @@
 #define true 1
 #define false 0
 #elif defined(__GNUC__) && !defined(__STRICT_ANSI__)
-/* Define _Bool, bool, false, true as a GNU extension. */
+/* Define _Bool as a GNU extension. */
 #define _Bool bool
+#if __cplusplus < 201103L
+/* For C++98, define bool, false, true as a GNU extension. */
 #define bool  bool
 #define false false
 #define true  true
 #endif
+#endif
 
 #define __bool_true_false_are_defined 1