This updates all targets to also extract the SP out of the
jmp_buf.

I peeked into glibc's, netbsd's, openbsd's and freebsd's sources
to get the SP offsets.  I also google.com/codesearch'ed quite a bit.
I looked manually for the offsets in cygwin, mingw32, and WinCE.

There are a couple I couldn't find any reference or sources to
look at, these were: 

- alpha-OSF1, I infered from the alpha BSD targets.
- QNX NTO, I guessed based on the other i386 ports that used
the same JB_PC.

- arm-linux: either we have currently the wrong jb_pc, or there must
  be some switch that changes the jmp_buf format I'm not aware of.  I
  took the values in the patch from glibc, and tested it with a
  qemu in several multilibs configurations, including -mthumb.
  Inspecting manually revealed that indeed the these are the
  correct values, and running the new longjmp.exp test passed cleanly.

- go32/djgpp claims jb_pc == 36, but, that's not what I see
  in the sources:
http://www.delorie.com/bin/cvsweb.cgi/djgpp/src/libc/ansi/setjmp/setjmp.S?rev=1.3
  Patch updates jb_pc to 32 as per that link.

Of course, I may have gotten a few wrong.

-- 
Pedro Alves