The first, possibly most important step in cleaning up DECR_PC_AFTER_BREAK's
tentacles. This changes handle_inferior_event to fix the PC immediately,
before doing anything else with it. It removes the later decrements, but
doesn't remove all the later workarounds for possibly undecremented PC
values - that can come separately.
One case, HANDLE_NONSTEPPABLE_WATCHPOINTS and DECR_PC_AFTER_BREAK, is simply
removed. There are no targets using this combination, and if one is added,
it's non-obvious whether a nonsteppable watchpoint really should be affected
by DECR_PC_AFTER_BREAK.
A future cleanup will change bpstat_stop_status to only take a CORE_ADDR
argument. Also, I believe that both the tests for sigtramps and the use of
deprecated_frame_update_pc_hack can go now, but I don't want to mix that in
with this - esp. since I'm not sure how to test the former belief.