Use bool return

Author: ldionne

libcxx/include/__locale

@@ -516,7 +516,7 @@ protected:
 };
 #endif // _LIBCPP_HAS_WIDE_CHARACTERS
 
-inline _LIBCPP_HIDE_FROM_ABI int __libcpp_isascii(int __c) { return (__c & ~0x7F) == 0; }
+inline _LIBCPP_HIDE_FROM_ABI bool __libcpp_isascii(int __c) { return (__c & ~0x7F) == 0; }
 
 template <>
 class _LIBCPP_EXPORTED_FROM_ABI ctype<char> : public locale::facet, public ctype_base {