Subzero: Fix "make -f Makefile.standalone MINIMAL=1 check".

Subzero: Fix "make -f Makefile.standalone MINIMAL=1 check".

Some recent ARM changes turned out to break the lit tests for the MINIMAL build.  Two main issues:

1. ARM tests are currently asm-only, so allow_dump needs to be required.

2. GlobalContext::emitFileHeader() needs to return gracefully instead of calling report_fatal_error(), to allow error tests to produce the right error output.

BUG= none
R=kschimpf@google.com

Committed: https://gerrit.chromium.org/gerrit/gitweb?p=native_client/pnacl-subzero.git;a=commit;h=c8799688d288c9acd71f0b4f193f9b1beac751aa

[Jim Stichnoth, 2015-06-22 19:51:34]

stichnot@chromium.org changed reviewers:
+ jpp@chromium.org, jvoung@chromium.org, kschimpf@google.com

[Karl, 2015-06-22 20:00:22]

lgtm

[Jim Stichnoth, 2015-06-22 20:04:15]

Committed patchset #1 (id:1) manually as
c8799688d288c9acd71f0b4f193f9b1beac751aa (presubmit successful).