go/buildutil: TagsFlag provides a flag.Value for setting build.Context.BuildTags from -tags flag.

Add -tags flag to oracle, ssadump, callgraph, gomvpkg, gorename, eg.

Change-Id: I4a818501b2331c4ea589caca37a3ad9d381dc8af
Reviewed-on: https://go-review.googlesource.com/9172
Reviewed-by: David Crawshaw <crawshaw@golang.org>
8 files changed