Teach autoninja.py to support GOMA_DISABLED env var
Teach autoninja.py to support GOMA_DISABLED env var

When GOMA_DISABLED is set goma will use the local compiler. Autoninja
needs to understand this in order to avoid requesting too much
parallelism.

Change-Id: Ic124893dd583a401d0d9ad7fbd27ee9b6715fcfe
Reviewed-on: https://chromium-review.googlesource.com/1015402
Commit-Queue: Bruce Dawson <fe9e26f3989304bf7275ed139c57fd059c63d22d@chromium.org>
Reviewed-by: Dirk Pranke <6693ee08b084bb2ffa767f664c99b689395e0e4b@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools