gfileutils: Fix O_NOFOLLOW handling on BSD systems

Merged Philip Withnall requested to merge wip/pwithnall/bsd-nofollow into master

Various different BSD systems use a different errno from E_LOOP (as defined by POSIX and used on Linux) to indicate that a file is a symlink when you try to open() it with O_NOFOLLOW.

Fix the code which detects this. This is a follow-up to #1302 (closed).

Signed-off-by: Philip Withnall

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