PR threads/2015: Fix adjust_pc_after_break for thread debugging

[Mark Kettenis]

> X-From_: gdb-patches-return-40942-m.m.kettenis=alumnus.utwente.nl@sources.redhat.com  Wed Sep 28 00:10:41 2005
> From: Andreas Schwab <schwab@suse.de>
> Date: Wed, 28 Sep 2005 00:10:18 +0200
> 
> adjust_pc_after_break is doing the wrong thing during thread debugging
> when the current thread is different from the thread when the debuggee was
> stopped last.  The problem is that it calls currently_stepping, which
> accesses global variables that are part of the thread context.  But the
> context switch will only happen much later on.  The proposed fix will skip
> the call when the current infrun context does not match the thread to be
> examined.  This has been tested on x86_64-suse-linux and fixes 32
> testcases without any regressions.

I'd really like to see this tested on some more systems though,
especially on systems where adjust_pc_after_break is a no-op and
systems with software single-step.

I can run a few tests later this week if you want.

Mark