[PATCH] Sanitize gdbarch access on probe/SDT API

[Tom Tromey]

Sergio> As it turns out, I saw Tom's approach to make probes program-space
Sergio> independent, and my patch touches many points that are also touched by
Sergio> Tom's.  Therefore, I will wait until he commits his patches, and then
Sergio> I'll rebase this one on top of them and resubmit.

Don't wait -- those patches depend on the minsym series.
I don't plan to check that in until 7.7, since it seems imminent,
since the minsym series is fairly large, and since the series could
probably use more testing on hosts that I don't have access to.

Tom