[PATCH,rs6000,PING] add support for generating out-of-line register saves/restores

[Nathan Froyd]

Ping:

http://gcc.gnu.org/ml/gcc-patches/2008-04/msg01678.html

with a small follow-up patch to fix a latent bug:

http://gcc.gnu.org/ml/gcc-patches/2008-04/msg01737.html

Patch was bootstrapped on SPE and PPC64 linux targets as well as PPC
Darwin.

Thanks,
-Nathan