libaom: run git cl format

Attempt to run 'git cl format' when updating configuration files.

R=tomfinegan@chromium.org

Change-Id: Ib78ac4df3f36361d72a2fa672a2382e68a5e188f
Reviewed-on: https://chromium-review.googlesource.com/1142432Reviewed-by: Tom Finegan <tomfinegan@chromium.org>
Commit-Queue: Johann Koenig <johannkoenig@google.com>
Cr-Commit-Position: refs/heads/master@{#576191}

third_party/libaom/cmake_update.sh

@@ -167,4 +167,6 @@ gen_config_files linux/arm64 "${toolchain}/arm64-linux-gcc.cmake ${all_platforms
 cd "${SRC}"
 update_readme
 
+git cl format &> /dev/null || echo "ERROR: Run 'git cl format' manually."
+
 clean