Propagate exit code in download_nacl_toolchains.

Bug: 787002
Change-Id: I4b7bd26638bb5dffccb52e6d2a06b8cc92ac6f41
Reviewed-on: https://chromium-review.googlesource.com/779626Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517902}

build/download_nacl_toolchains.py

@@ -52,9 +52,7 @@ def Main(args):
   if 'target_arch=arm' not in os.environ.get('GYP_DEFINES', ''):
       args = ['--exclude', 'nacl_arm_newlib'] + args
 
-  package_version.main(args)
-
-  return 0
+  return package_version.main(args)
 
 
 if __name__ == '__main__':