Update libglnx subproject
Update libglnx subproject

* Improve compatibility with eCryptFS (related to #4673)
* Improve compatibility with copying pseudo-files from /proc
* Add a flag to skip fchown() in glnx_file_copy_at()
* Add a rewinddir() wrapper to GLnxDirFdIterator
* Rename its generated config header to libglnx-config.h
* Fix a potential double-free while manipulating xattrs
* Use REUSE for copyright/licensing statements

Note that after merging this in an existing checkout, it will be
necessary to re-run autogen.sh.

Signed-off-by: Simon McVittie <0e1aea601907c1a85c2dc96e5ea37e23c58d2e9b@collabora.com>

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