fix Guile headers

Guile headers include a #define for noreturn:

  #define SCM_NORETURN __attribute__ ((noreturn))

which is a problem when other headers have a #define
for "noreturn".

* autoopts/fix-guile.sh: new script that fixes the Guile define
  to replace "(noreturn)" with "(__noreturn)".
* autoopts/bootstrap.dir: distribute the stinky thing
* autoopts/Makefile.am: run the stinky thing when needed
* config/misc.def: run the gl_STDNORETURN_H macro in configure
* agen5/scribble.c : Warning patrol
Do not abort from main()

If you are going to create a core dump, keep the stack active
and correct.

* agen5/autogen.c: remove abend_env and abend_sig globals
  (main): remove sigsetjmp call
  (cleanup_and_abort): mark with _Noreturn
  (ag_abend_at): likewise