Recent linux kernel bug causing problem for xkbcomp

[walt]

Hi team.  I'm trying to debug a recent commit to Linus's git repo
that causes startx to halt with a complaint that it can't write a
.xkm file to /var/lib/xkb.

I'm assuming that the message is from xkbcomp, but I can't find
where in the startx process that xkbcomp is run, or what else might
produce such an error message.  I'd like to reproduce the error by
running xkbcomp manually so I can track it down.

Even vague and generic hints might be helpful :)

Thanks!