Continuations capture machine code address

* libguile/continuations.c (scm_i_continuation_to_frame): Adapt to vra
  field renaming.
  (scm_i_reinstate_continuation, grow_stack, copy_stack_and_call)
  (scm_dynthrow): Take mra of continuation.  Set on the vp before the
  longjmp.
* libguile/continuations.h: Update scm_i_reinstate_continuation
  prototype.
* libguile/dynstack.h:
* libguile/control.c (scm_suspendable_continuation_p):
* libguile/dynstack.c (PROMPT_WORDS, PROMPT_VRA, PROMPT_MRA):
  (PROMPT_JMPBUF, scm_dynstack_push_prompt, scm_dynstack_find_prompt)
  (scm_dynstack_wind_prompt): Store both virtual and machine return
  addresses on the dynstack, for prompts.
* libguile/eval.c (eval): Pass NULL for mra.
* libguile/intrinsics.c (push_prompt): Add mra arg, and pass it to the
  dynstack.
* libguile/intrinsics.h: Update prototypes so that continuation-related
  intrinsics can save and restore the MRA.
* libguile/jit.h:
* libguile/jit.c: Return VRA when JIT code needs to tier down.
* libguile/stacks.c (find_prompt, scm_make_stack)
* libguile/throw.c (catch): Adapt find-prompt calls.
* libguile/vm-engine.c (instrument-entry, instrument-loop): Add logic to
  continue with vcode after the mcode finishes.
  (compose-continuation, capture-continuation, abort, prompt): Add logic
  to pass NULL as captured MRA, but continue with mcode from new
  continuations, if appropriate.
* libguile/vm.c (scm_i_vm_cont_to_frame, capture_stack)
  (scm_i_capture_current_stack, reinstate_continuation_x)
  (capture_continuation, compose_continuation_inner, compose_continuation)
  (capture_delimited_continuation, abort_to_prompt): Adapt to plumb
  around machine code continuations.
  (scm_call_n): Check "mra_after_abort" field for machine code
  continuation, if any.
* libguile/vm.h (struct scm_vm): Add "mra_after_abort" field.
  (struct scm_vm_cont): Rename "ra" field to "vra" and add "mra" field.

libguile/control.c

@@ -138,7 +138,7 @@ scm_suspendable_continuation_p (SCM tag)
   jmp_buf *registers;
 
   if (scm_dynstack_find_prompt (&thread->dynstack, tag, &flags,
-                                NULL, NULL, NULL, &registers))
+                                NULL, NULL, NULL, NULL, &registers))
     return scm_from_bool (registers == thread->vm.registers);
 
   return SCM_BOOL_F;