Make win_as.py notice and report errors better

Make win_as.py notice and report errors better

The win_as.py script completely hides errors from running
cl.exe (the C preprocessor) and while it displays errors from
running the assembler, it hides the exit status of the assembler so
the script returns success even if the commands it ran failed.

Fix this by detecting the exit status from running cl.exe and
displaying its stderr when there was an error, and by detecting
the exit status from running the assembler, and having the script
exit with failure if either command failed.

BUG=512869
TEST= trybots
R=bradnelson@chromium.org, scottmg@chromium.org

Committed: https://chromium.googlesource.com/native_client/src/native_client/+/ba703459e79eb73b9a7a2bf9b1ca644106e20a9f

[bradnelson, 2015-11-04 22:57:56]

The CQ bit was checked by bradnelson@chromium.org

[bradnelson, 2015-11-04 22:57:56]

lgtm

[commit-bot: I haz the power, 2015-11-04 22:58:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1415983005/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1415983005/1

[scottmg, 2015-11-04 23:08:40]

lgtm

https://codereview.chromium.org/1415983005/diff/1/tools/win_as.py
File tools/win_as.py (left):

https://codereview.chromium.org/1415983005/diff/1/tools/win_as.py#oldcode91
tools/win_as.py:91: if p.wait() == 0: # success
Although I see it was already like this. Well.

https://codereview.chromium.org/1415983005/diff/1/tools/win_as.py
File tools/win_as.py (right):

https://codereview.chromium.org/1415983005/diff/1/tools/win_as.py#newcode75
tools/win_as.py:75: cl_status = p.wait()
It's weird to communicate() and then wait() as they both wait for termination.
This should just be cl_status = p.returncode.

https://codereview.chromium.org/1415983005/diff/1/tools/win_as.py#newcode111
tools/win_as.py:111: as_status = p.wait()
Same.

[commit-bot: I haz the power, 2015-11-04 23:10:41]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-11-04 23:10:41]

Try jobs failed on following builders:
  nacl-win64_newlib_opt on tryserver.nacl (JOB_FAILED,
http://build.chromium.org/p/tryserver.nacl/builders/nacl-win64_newlib_opt/bui...)

[Roland McGrath, 2015-11-04 23:15:34]

https://codereview.chromium.org/1415983005/diff/1/tools/win_as.py
File tools/win_as.py (right):

https://codereview.chromium.org/1415983005/diff/1/tools/win_as.py#newcode75
tools/win_as.py:75: cl_status = p.wait()
On 2015/11/04 23:08:40, scottmg wrote:
> It's weird to communicate() and then wait() as they both wait for termination.
> This should just be cl_status = p.returncode.

Done.

https://codereview.chromium.org/1415983005/diff/1/tools/win_as.py#newcode111
tools/win_as.py:111: as_status = p.wait()
On 2015/11/04 23:08:40, scottmg wrote:
> Same.

Done.

[Roland McGrath, 2015-11-04 23:18:29]

Committed patchset #2 (id:20001) manually as
ba703459e79eb73b9a7a2bf9b1ca644106e20a9f (presubmit successful).