[RFC] frame-ify the alpha port

[Richard Henderson <rth at twiddle dot net>]

I got started down this path because the last time I tried 
to use cvs gdb, it crashed immediately.  Some conversation
with Andrew at the gcc summit this week inspired me to do
more than paper over whatever segv I'd been seeing.

Test results with this patch are still abysmal, but 
backtraces work correctly on two minimal tests that I
examined -- including backtracing through signal frames,
which I know *didn't* work before.

The major changes are:

  (1) Move all mdebug dependencies into alpha-mdebug-tdep.c.

  (2) Create three different unwinders, anchored with
	alpha_mdebug_frame_p
	alpha_sigtramp_frame_p
	alpha_heuristic_frame_p

      All of this code existed in the old routines, scattered
      about alpha_find_saved_regs, heuristic_proc_desc, 
      find_proc_desc, and alpha_frame_chain.  But much harder
      to suss out what's what.

I had been thinking to do some of this in stages, so that it
would be easier to see what I was doing, but it kind of got
out of hand.

Mostly what I'm looking for here is whether or not I've 
properly understood The Way of Frame Unwinding.


r~

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