fix(fs.c, windows, ucrt64): fix getcwd for windows ucrt64 builds

[NaitLee]

I'm really late 🥲 With this patch, compiling darkplaces master with msys2 ucrt64 environment is back to normal.

History:

• A commit was introduced to have current working directory known by the engine to fix some mods:
  • https://gitlab.com/xonotic/darkplaces/-/commit/1f4743e930b01c520372c570fb6c936ed461ee64
  • To fix: modlist.txt looks for mods in c:\ on windows #172
• I submitted a patch, because that code breaks games in Windows non-ascii paths:
  • https://gitlab.com/xonotic/darkplaces/-/merge_requests/153
• The _getcwd function used in the patch is causing segmentation fault in ucrt64 environment:
  • https://gitlab.com/xonotic/darkplaces/-/issues/422
• We need a win32 native function to avoid this segmentation fault — this pull request

Closes gitlab.com/xonotic/darkplaces#422.

[divVerent]

This should be sizeof(fs_basedirw) / sizeof(*fs_basedirw), so that the elements, not bytes, are counted.

[NaitLee]

You are right. New commit pushed to fix this.

[divVerent]

wasm error seems unrelated.

As for _wgetcwd vs GetCurrentDirectoryW - I still am not convinced that was the problem, but at the same time, don't care. The winapi function name is slightly more readable than the not-really-posix name, both are proprietary, so may as well keep the winapi one you got there.