This change refactors the call to `git-describe` made in `//:Makefile`,
such that if the call made to populate the `GitLastTag` build argument
fails for any reason, the value is an empty string.

This resolves a fairly common situation in CI, and reproducible
elsewhere, if the local repository does not have any tags.

Change-Id: Ie8e06360d5a4016596b96c6371ce4e32ad6a8afb

marked this pull request as ready for review

sudoforge deleted the Ie8e06360d5a4016596b96c6371ce4e32ad6a8afb branch