Make autoninja.py handle git bash better

If autoninja.py detects that goma is not running when it should be then
it prints 'cmd /c exit 1' as the command to be run. This ensures that
errorlevel will be set so that the failure will be detected.
Unfortunately this doesn't work when running autoninja from git bash.
Instead of launching a cmd.exe instance which immediately exits, it
launches a cmd.exe instance which the user must manually exit.

This change adds quotes so that this works from git bash (which invokes
the shell script) as well as from cmd.exe (invoking the batch file).

Bug: 868590
Change-Id: I482f22830f9bd4f7b70c51de9647a70d946ec145
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2726085
Reviewed-by: Joe Mason <joenotcharles@chromium.org>
Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Owners-Override: Bruce Dawson <brucedawson@chromium.org>
Auto-Submit: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@google.com>

autoninja.py

@@ -132,7 +132,7 @@ if use_goma:
             file=sys.stderr)
       if sys.platform.startswith('win'):
         # Set an exit code of 1 in the batch file.
-        print('cmd /c exit 1')
+        print('cmd "/c exit 1"')
       else:
         # Set an exit code of 1 by executing 'false' in the bash script.
         print('false')