Some filesystems don't have meaningful access times under at least some
circumstances (see #2189, #2205). In this situation the traditional stat()
and related kernel interfaces have to put something meaningless in the
st_atime field, and have no way to signal that it is meaningless.

However, statx() does have a way to signal that the atime is meaningless:
if the filesystem doesn't provide a useful access time, it will unset
the STATX_ATIME bit (as well as filling in the same meaningless value
for the stx_atime field that stat() would have used, for compatibility).
We don't actually *need* the atime, so never include it in the required
mask. This was already done for one code path in commit 6fc143bb
"gio: Allow no atime from statx" to fix #2189, but other callers were
left unchanged in that commit, and receive the same change here.

It is not actually guaranteed that *any* of the flags in the
returned stx_mask will be set (the only guarantee is that ...