Note in PPCFunctionInfo VRSAVE spills

In preparation for using the new register scavenger capability for providing
more than one register simultaneously, specifically note functions that have
spilled VRSAVE (currently, this can happen only in functions that use the
setjmp intrinsic). As with CR spilling, such functions will need to provide two
emergency spill slots to the scavenger.

No functionality change intended.
PPC ZERO register needs a register number of 0.

In order for the new ZERO register to be used with MC, etc. we need to specify
its register number (0).

Thanks to Kai for reporting the problem!