Merged new upstream libunwind code

[Mark Wielaard <mark@klomp.org>]

Hi,

Since there was a huge commit in upstream libunwind that overlaps a bit
with some of our patches I imported it and merged it with our code. It
does also contains two of our patches so some of the divergence has come
down again.

It contains some support for local debug_frame parsing support.
Unfortunately that bites our remote debug_frame parsing a bit. I added
comments where our approach is different from upstream or the
assumptions don't hold for our remote case. I didn't try use some of the
new parsing code introduced since our current approach works just fine
for the remote case.

It also contains support for ARM and MIPS. This isn't being compiled yet
in our tree (only x86, x86_64, ppc and ppc64 is).

Tested on x86 and x86_64 and no regressions in our testsuite.
But there is one extra failure in the libunwind testsuite (a local
failure) that needs investigating (you normally won't see it unless you
configure --enable-check-libunwind --enable-debug).

Cheers,

Mark