headers: Temporarily undefine _Bool when typedeffing std::_Bool

This fixes building the following with libc++:

With libc++, yvals.h is implicitly included by anything that includes
locales (via xlocinfo.h).

Signed-off-by: Martin Storsjö <martin@...>

Upstream URL:
https://sourceforge.net/p/mingw-w64/mingw-w64/ci/0e19d55353d81f1ead81ce590e618d47f9c12331/

Change-Id: I181892e94128a0941911eb815a0aebb9e1a65981
diff --git a/mingw-w64-v5.0.0/mingw-w64-headers/crt/yvals.h b/mingw-w64-v5.0.0/mingw-w64-headers/crt/yvals.h
index 70593c4..15130e4 100644
--- a/mingw-w64-v5.0.0/mingw-w64-headers/crt/yvals.h
+++ b/mingw-w64-v5.0.0/mingw-w64-headers/crt/yvals.h
@@ -163,9 +163,12 @@
 #define _Restrict __restrict__
 
 #ifdef __cplusplus
+#pragma push_macro("_Bool")
+#undef _Bool
 _STD_BEGIN
 typedef bool _Bool;
 _STD_END
+#pragma pop_macro("_Bool")
 #endif
 
 #define _LONGLONG /* __MINGW_EXTENSION */ __int64