Add a workaround for MinGW version mismatches in GHC and the Platform.

MinGW's <sys/stat.h> requires __MSVCRT_VERSION__ >= 0x0601 to define
_wstat64(). This is fine for the MinGW distributed with GHC, which sets
__MSVCRT_VERSION__ = 0x0700, but fails for the Haskell Platform because
its MinGW sets __MSVCRT_VERSION__ = 0x0600.

Therefore, we include <_mingw.h> first and bump its MSVCRT if necessary.
Bump version to 0.3.14