Changes so we can cross-compile from x86 to ppc. This will produce a

core that appears to work.  More testing needed.

src/compiler/ppc/c-call.lisp:
o Use the old vops that only store floats in float registers.  We
  don't need them also stored in integer registers.  This causes an
  error during cross-compile about %NL1 conflicting with a wired tn.

src/tools/cross-scripts/cross-x86-ppc-darwin.lisp:
o Copy over similar features from cross-x86-sparc.lisp so that the
  cross-compile will work.