base

Run doc-comment-check only for checkbuild.

Currently doc-comment-check is the single longest-running process during
the make process. It usually takes 300-400s to finish on my Z600.
What's worse, it's usually the last straggler build job.
Not running this by default can save big build time.

Bug: 7253452
Change-Id: Idc868197b59e42c6b583c66f13a0e6a1bc8d5d4e