Fix binary instructions to accept flags argument in pnacl-bcdis.

Fixes bug where some old PNaCl PEXE files had binary instructions
with 4 arguments instead of 3. The fourth argument is a "flags" argument
that should be ignored.

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4364
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1844563003 .
4 files changed