perlasm/arm-xlate.pl update (fix end-less loop and prepare for 32-bit iOS).

(Imported from upstream's 7b644df899d0c818488686affc0bfe2dfdd0d0c2)

Looking at update_gypi_and_asm.py with git diff -w, the only differences seem
to be that .asciz fixed a bug where a space after a ',' got swallowed (sigh).

BUG=338886

Change-Id: Ib52296f4a62bc6f892a0d4ee7367493a8c639a3b
Reviewed-on: https://boringssl-review.googlesource.com/4480
Reviewed-by: Adam Langley <agl@google.com>