FileSystem: Use _stat64 routines

[xantares]

allows compilation with gcc/mingw

[lightningterror]

@xantares Status?

[xantares]

@lightningterror this is still needed

[lightningterror]

Closing for the reasons stated before.

[xantares]

@lightningterror what if I drop that commit ? the rest should be good

[stenzek]

I don't know why we would want to build with mingw anyway. There's plenty of issues with headers being out of date, subtle ABI differences, and it provides no advantage.

I have a branch with clang-cl support, which if you want to use non-MSVC codegen, works much better.

Edit: Probably should mention that once #7295 merges, it'll be using functions from Win10 1803 which might not be available, so it'll just break again. Plus the fact that our Qt builds are not for gcc, they're for msvc.