winpthreads: Always define `__USE_MINGW_ANSI_STDIO` to zero

In the x86 case, mingw-w64 stdio functions use 64-bit division, which
relies on certain routines in libgcc, and causes undefined references
under some circumstances.

Instead, the MS ones should be called, which are available immediately
and do not depend on libgcc. This was also the case prior to bfd33f6c.

Reference: https://github.com/msys2/MINGW-packages/pull/6539
Signed-off-by: Liu Hao <lh_mouse@126.com>