x/build: all-compile builder only do weird things

The `all-compile` builder is pretty slow. It should only compile things which aren't otherwise covered by other trybots. Most of the work it does is redundant.

Plan: let buildall.sh take arguments.  (list of things to do? things to NOT do, so we don't miss new things later?)  List of things to do is probably easier and cleaner.

Then modify dashboard/builders.go and support setting args to it.
