Crash in jit-ucs-charset handling

[Stephen J. Turnbull]

Aidan Kehoe writes:

 > On the minus side; I can’t reproduce it on NetBSD, even with what should be
 > an identical build to yours, so I can’t easily investigate further ... hmm,
 > actually, wait. Is it possible for Fcharset_matches_specifier_tag_set_p to
 > be called recursively? What’s the full C backtrace?

I don't have it; that box needed rebooting for security update and it
was too late to be thinking straight, I just wanted to go to bed.
I'll see if I can get it to happen tonight; it's presumably data
dependent.