Fix and clean up intrinsic Math.abs(long).

On ARM, make sure we don't clobber a register that we still
need for the next insn. On x86, don't free a source register
for temps if it's overlapping a result register as that
would allow the sign_reg temporary to alias with the result.

Change-Id: I785f2f607900ae8ceb2fa0b8f3eefafdf6fab5c7