The integrated ARM assembler was incorrectly assuming that an
(instruction) label defines a corresponding assembler instruction.
Therefore, placement into the buffer was incorrect.

This CL fixes this mistake. This fixes assembler translator problems
with ARM branch, movw, and movt instructions.

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4334
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1430973003 .