while the incorporation of this requirement from C99 into C++11 was
likely an accident, some software expects it to be defined, and it
doesn't hurt. if the requirement is removed, then presumably
__bool_true_false_are_defined would just be in the implementation
namespace and thus defining it would still be legal.
#define false 0
#define bool _Bool
-#define __bool_true_false_are_defined 1
-
#endif
+#define __bool_true_false_are_defined 1
+
#endif