Fix bug in arith.ll (ARM) tests.

Fix bug in arith.ll (ARM) tests.

CL https://codereview.chromium.org/1687553002 introduced a bug when
running:

   make -f Makefile.standalone check-lit FORCEASM=1

The cause of the problem is the way options "--asemble --disassemble"
work in run-pnacl-sz.py. When compiling using "--filetype=asm", the
assembler writes:

   .word 0xe7fedef0

The output after assembly/disassembly is the same as above.

On the other hand, when compiling using "--filetype=iasm", the assembler
writes:

   .byte 0xe7
   .byte 0xfe
   .byte 0xde
   .byte 0xf0

While the same sequence of bytes is assembled, the dissassembly for the
latter generates assembly instruction:

    udf #60896 ; 0xede0

The fix is to not check the generated disassembled instructions. Rather,
have it check if the same word is associated with the assembly
instruction.

Longer term, we should fix the several different ways --filetype=asm
introduces this instruction to match the "udf ..." output.

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4076
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1682253003 .