compiler_version: suppress stdout unless command fails

compiler_version: suppress stderr unless command fails

gyp considers a shell variable substitution to have failed if it
generates any output to stderr, even if the exit status was zero.
This causes problems when gomacc automatically starts its proxy,
which helpfully reports "GOMA: Starting compiler proxy" to stderr.

Fixed by dropping stderr unless the underlying process returns
a non-zero exit status.

BUG=chromium-os:28670
TEST=Ran hooks normally and inside CrOS chroot, with and without
  $CXX pointing to goma. A $CXX which writes to stderr and then
  exits with failure still prints its output before the exception.


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=135663

[cwolfe, 2012-05-01 22:38:23]

maruel: Hope you don't mind being drafted for a quick review; this file doesn't
seem much traffic.

Quick fix for an issue we've been hitting on manual CrOS builds with goma, since
nobody ever remembers to start the proxy manually. I'm half inclined to report
it as a bug against gyp, but fixing here also seems reasonable.

In a few other places we call pipe.wait() after a .communicate(), which the docs
suggest is unnecessary.

[M-A Ruel, 2012-05-07 15:31:34]

lgtm

[cwolfe, 2012-05-07 15:44:21]

On 2012/05/07 15:31:34, Marc-Antoine Ruel wrote:
> lgtm

Thanks! Suspect it'll need a rebase, but will let the CQ have a look first.

[commit-bot: I haz the power, 2012-05-07 15:44:27]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/cwolfe@chromium.org/10288005/1

[commit-bot: I haz the power, 2012-05-07 17:24:54]

Change committed as 135663