fix stack space calculation in compile-powerpc.S
fix stack space calculation in compile-powerpc.S

dicej/avian,getlantern/avian,ucdseniordesign/avian,dicej/avian,lostdj/avian,minor-jason/avian,minor-jason/avian,ucdseniordesign/avian,lwahlmeier/avian,lostdj/avian,bigfatbrowncat/avian-pack.avian,dicej/avian,badlogic/avian,ucdseniordesign/avian,bgould/avian,bgould/avian,badlogic/avian,joshuawarner32/avian,getlantern/avian,minor-jason/avian,joshuawarner32/avian,ucdseniordesign/avian,lwahlmeier/avian,marcinolawski/avian,badlogic/avian,lostdj/avian,bgould/avian,lwahlmeier/avian,marcinolawski/avian,bigfatbrowncat/avian-pack.avian,lostdj/avian,joshuawarner32/avian,joshuawarner32/avian,minor-jason/avian,bigfatbrowncat/avian-pack.avian,badlogic/avian,MaartenR/avian,bgould/avian,dicej/avian,marcinolawski/avian,MaartenR/avian,getlantern/avian,MaartenR/avian,MaartenR/avian,lwahlmeier/avian,marcinolawski/avian,bigfatbrowncat/avian-pack.avian,getlantern/avian