Blender Git Loki

Windows: Replace BLI_File* calls with system calls in system_win32.c

Using BLI calls in this file triggered a condition where
poorly modelled dependencies in cmake (ie bf_blenlib using
zlib headers but not linking the libraries) leading to
linker error in debug builds of some of the tests.

This diff sidesteps the dependencies issue by using native
calls rather than BLI calls to check if a file exists and
what its size is. Effectively sweeping the issue right back
under the rug where I found it.

The best solution would be to audit all libraries and ensure
they have proper link requirements set, but that requires
significantly more time than I have available right now.
(zlib in blenlib was one of them and would have been easy
to fix, but there were others that required more work)

The alternative is tests that fail to build which worse.

I'll revisit this and fix it properly but for now this will
have to do.