0/5 - longjmp rework

[Pedro Alves]

This series of patches reworks the stepping over longjmp support,
and fixes a couple of targets on the way.  This rework started
by making stepping over longjmp work correctly in non-stop mode,
and then extended into fixing the longjmp support properly.

Having longjmp working nicelly is very helpful when
debugging GDB, as our exceptions model is implemented
on top of setjmp/longjmp.  It's nice to step over a
throwing function, and have the step land at the catch
site.

The patches are:

 1/5 - remove BPSTAT_WHAT_CLEAR_LONGJMP_RESUME_SINGLE
 remove_longjmp_single.diff

 2/5 - add basic longjmp testing to the testsuite
 longjmp_tests.diff

 3/5 - Rework stepping over longjmp support
 longjmp_rewrite.diff

 4/5 - fix/implement x86_64 gdbarch_get_longjmp_target
 longjmp_amd64.diff

 5/5 - handle glibc pointer mangling jmp_bufs (x86/x86_64)
 longjmp_linux_x86_amd64_pointer_demangle.diff


The whole series was tested on x86_64-unknown-linux-gnu
and x86-pc-linux-gnu, and x86-pc-cygwin.

-- 
Pedro Alves