implement syncInstructionCache for ARM
implement syncInstructionCache for ARM

Like, PowerPC, ARM has an instruction cache which must be manually
flushed if/when we compile a new method.  This commit updates
syncInstructionCache to use GCC's builtin __clear_cache routine.

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