cmd/coordinator: add flag to specify which branches to watch

gcc has about 150 or so branches and we only care about one of them
so for gccgo's watcher, the option to specify which branch to watch
is necessary.

Change-Id: I34cf95d3f6925d57833e2ebdb6134ac4a81b05ba
Reviewed-on: https://go-review.googlesource.com/16082
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed