[avr] fixup dwarf2 unwind info

[Denis Chertykov]

2011/3/21 Richard Henderson <rth@redhat.com>:
> This is a slightly tidied patch from sometime last month, which was
> buried in a thread about dwarf2 unwind info for gas.  This fixes
> some totally incorrect unwind markings in the avr backend, and adds
> support in the dwarf2 middle-end for handling avr's unique post_dec
> (rather than pre_dec) push insns.
>
> Ok to commit?
>

Please, commit.

Denis.