[patch/rfa/hppa] Use frame pointer for unwinding

[Andrew Cagney]

26. alloca_frame (bit 35): This bit is set if alloca() is used and has 
been inlined. This indicates gr3 or gr4 may contain the previous sp 
value.

For some reason this latter flag is named differently in the gdb sources
compared to what's in the documentation.
(feel free to fix)

Anyway, I spoke with Dave Anglin (hppa gcc maintainer) about this. The
problem is that currently gcc/binutils does not correctly implement the
alloca_frame bit. The frame pointer is maintained in the case of a
variable-sized frame, but there is no flag set in the unwind record, and
the frame layout is slightly different compared to the HP compiler. It's
one of the things that should be fixed in gcc eventually. Also Dave has
observed that the Save_SP bit is set only for gcc; with the HP compiler
this is not set.  Finally, with the HP compiler the frame pointer can 
be maintained either in r3 or r4. It's not clear yet how this works. 
Some more experimentation/disassembling HP code is required :-( 
I will add some comments to the code about this situation.
Is there a GCC bug report for this?

(more followups to come)

Andrew