mdbx-windows: refine mdbx_vasprintf() to avoid dependency from CRT.
mdbx-windows: refine mdbx_vasprintf() to avoid dependency from CRT.

10 of 17 for https://github.com/leo-yuriev/libmdbx/issues/43

Change-Id: I95c4583c27503eb4e9221b212b34474dfb561e6d

leo-yuriev/libfpta,leo-yuriev/libfpta