Fix compilation of the directory iteration code on additional POSIX based platforms

[s-ludwig]

See #242

[Geod24]

source/vibe/core/file.d(1065,46): Error: undefined identifier `AT_SYMLINK_NOFOLLOW`
source/vibe/core/file.d(1048,17): Error: undefined identifier `timespec`
source/vibe/core/file.d(1059,12): Error: static assert:  "Found no nanoseconds fields in struct stat"
source/vibe/core/file.d(1072,24):        instantiated from here: `getTimeField!"st_mtim"`
dmd failed with exit code 1.

#250

I fixed the AT_SYMLINK_NOFOLLOW upstream but you'll need a workaround for the time being.

[s-ludwig]

Cherry picked the workflow commit from #250 and fixed another error.

[s-ludwig]

Okay, not sure what was going on with timespec, but it's now down to this:

Linking...
cc: No such file or directory
Error: linker exited with status 255

[s-ludwig]

Okay, let me just drop the workflow commit, so that this can get merged and then #250 is the one that adds the workflow...