MIPS64: some very minor todo cleanups.
MIPS64: Fix gap resolver moves to stack slots for local variables.

This fixes zlib dead loop execution bug and mjsunit/md5 random failure.

TEST=mjsunit/md5
BUG=
MIPS64: Disable usage of cacheflush user space builtin in android for MIPS64.

This is set according to current state in chromium for android.