Switch from defaulting to the 'local' spiller to the 'simple' spiller. The

two spillers produce perfectly identical code (at least on povray and eon),
but the simple spiller is substantially faster than the local spiller. Once
the local spiller is improved, we can switch back.

Switching cuts 5.2% off of the llc time for povray (about 1.3s).

llvm-svn: 16608