_mingw.h: Do not check for _UCRT

This fixes commit bfd33f6c0ec5e652cc9911857dd1492ece8d8383. _UCRT does not
have to be defined yet (it is defined after including _mingw.h), but
__MSVCRT_VERSION__ at this stage is always defined (few lines above).

Signed-off-by: Liu Hao <lh_mouse@126.com>
1 file changed