Add Java toolchain to a genrule that requires it.
Add Java toolchain to a genrule that requires it.

Summary:
Since Bazel 0.10.0, it is now necessary to specify the toolchain explicitly in
order to get the $(JAVA) make variable defined.

Breaking change is breaking.

Reviewers: shahms, #core_team

Reviewed By: shahms, #core_team

Subscribers: #core_team

Differential Revision: https://phabricator-dot-kythe-repo.appspot.com/D2161

bzz/kythe,bzz/kythe,benjyw/kythe,benjyw/kythe,kythe/kythe,bzz/kythe,kythe/kythe,bzz/kythe,benjyw/kythe,bzz/kythe,benjyw/kythe,benjyw/kythe,bzz/kythe,benjyw/kythe,benjyw/kythe,kythe/kythe,bzz/kythe,kythe/kythe,kythe/kythe,benjyw/kythe,kythe/kythe,bzz/kythe,kythe/kythe,bzz/kythe,kythe/kythe,kythe/kythe,benjyw/kythe,kythe/kythe,kythe/kythe,benjyw/kythe,benjyw/kythe,bzz/kythe,bzz/kythe,bzz/kythe,benjyw/kythe