W32: Ensure that correct statting function is used by iconcache

W32: Ensure that correct statting function is used by iconcache

With Mingw-w64 fstat() can be an inline function that
calls _fstat32() or _fstat64(), depending on some macros.
And if LFS is enabled, fstat() is defined to turn into
_fstat32i64() or _fstat64(). And some/all of the above
might also be macros as well. Side-step all that mess
and excplicitly re-define fstat as _fstat32, which is
guaranteed to use a version of "stat" struct that
has 32-bit size and time fields, which is what we want.

https://bugzilla.gnome.org/show_bug.cgi?id=760615