Revert old nexti prologue check and eliminate in_prologue

Revert old nexti prologue check and eliminate in_prologue

The in_prologue check in the nexti code is obsolete; this commit
removes that, and then removes the in_prologue function as nothing
else uses it.

Looking at the code in GDB that makes use in_prologue, all we find is
this one caller:

      if ((ecs->event_thread->control.step_over_calls == STEP_OVER_NONE)
	  || ((ecs->event_thread->control.step_range_end == 1)
	      && in_prologue (gdbarch, ecs->event_thread->prev_pc,
			      ecs->stop_func_start)))
	{
	  /* I presume that step_over_calls is only 0 when we're
	     supposed to be stepping at the assembly language level
	     ("stepi").  Just stop.  */
	  /* Also, maybe we just did a "nexti" inside a prolog, so we
	     thought it was a subroutine call but it was not.  Stop as
	     well.  FENN */
	  /* And this works the same backward as frontward.  MVS */
	  end_stepping_range (ecs);
	  return;
	}

This was added by:

 commit 100a02e1deec2f037a15cdf232f026dc79763bf8
 ...
     From Fernando Nasser:
     * infrun.c (handle_inferior_event): Handle "nexti" inside function
     prologues.

The mailing list thread is here:

  https://sourceware.org/ml/gdb-patches/2001-01/msg00047.html

Not much discussion there, and no test, but looking at the code around
what was patched in that revision, we see that the checks that detect
whether the program has just stepped into a subroutine didn't rely on
the unwinders at all back then.

From 'git show 100a02e1:gdb/infrun.c':

    if (stop_pc == ecs->stop_func_start         /* Quick test */
        || (in_prologue (stop_pc, ecs->stop_func_start) &&
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            !IN_SOLIB_RETURN_TRAMPOLINE (stop_pc, ecs->stop_func_name))
        || IN_SOLIB_CALL_TRAMPOLINE (stop_pc, ecs->stop_func_name)
        || ecs->stop_func_name == 0)
      {
        /* It's a subroutine call.  */

        if ((step_over_calls == STEP_OVER_NONE)
            || ((step_range_end == 1)
                && in_prologue (prev_pc, ecs->stop_func_start)))
          {
            /* I presume that step_over_calls is only 0 when we're
               supposed to be stepping at the assembly language level
               ("stepi").  Just stop.  */
            /* Also, maybe we just did a "nexti" inside a prolog,
               so we thought it was a subroutine call but it was not.
               Stop as well.  FENN */
            stop_step = 1;
            print_stop_reason (END_STEPPING_RANGE, 0);
            stop_stepping (ecs);
            return;
          }

Stripping the IN_SOLIB_RETURN_TRAMPOLINE checks for simplicity, we had:

    if (stop_pc == ecs->stop_func_start         /* Quick test */
        || in_prologue (stop_pc, ecs->stop_func_start)
        || ecs->stop_func_name == 0)
      {
        /* It's a subroutine call.  */

That is, detecting a subroutine call was based on prologue detection
back then.  So the in_prologue check in the current tree only made
sense back then as it was undoing a bad decision the in_prologue check
that used to exist above did.

Today, the check for a subroutine call relies on frame ids instead,
which are stable throughout the function.  So we can just remove the
in_prologue check for nexti, and the whole in_prologue function along
with it.

Tested on x86_64 Fedora 20, and also by nexti-ing manually a prologue.

gdb/
2014-11-07  Pedro Alves  <palves@redhat.com>

	* infrun.c (process_event_stop_test) <subroutine check>: Don't
	check if we did a "nexti" inside a prologue.
	* symtab.c (in_prologue): Delete function.
	* symtab.h (in_prologue): Delete declaration.