Update libglnx, port various bits to new API

Update libglnx, port various bits to new API

Using the error prefixing in the delta processing allows us to
do new code style.  Also strip trailing whitespace.

Use error prefixing in a few other random places.  I didn't
hunt for all of them, just testing out the new API.

Use `glnx_fchmod()`.  Also note I dropped one `fchmod (tmpf, 0600)`
which is no longer necessary.

Update submodule: libglnx

Closes: #1011
Approved by: jlebon