glnx_file_copy_at: Add GLNX_FILE_COPY_NOCHOWN
In some contexts, we may want to copy a root-owned file but we're not
running as root so we can't fchown
it. (The case I'm interested in is
actually a bit more obscure than this: running in a supermin VM as root,
and wanting to copy a file we created onto a 9p mount where we don't
have perms to fchown
).
Add a GLNX_FILE_COPY_NOCHOWN
to handle this case.