[infra] Tweak compile_cas to work with other repos

Bug: skia:10883
Change-Id: I42d7b2926aaab2b76adf69162153a6a65998380d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/373742
Reviewed-by: Weston Tracey <westont@google.com>
Commit-Queue: Eric Boren <borenet@google.com>
1 file changed