cmd/go: add Mercurial based version stamping for binaries
This CL adds a local only VCS lookup for Mercurial.
It fixes a bug in pkg.go by passing in the repo directory to
the LookupLocal function instead of the module directory. It could be
the case that a binary is built in a subdirectory of the repo.
For: #50603
Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Change-Id: Ic36b5a361a8ba3b0ba1a6968cde5f5263c9c8dd0
Reviewed-on: https://go-review.googlesource.com/c/go/+/609155
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Michael Matloob <matloob@golang.org>