Make `git describe` versioning optional

We're building both development and release builds with detached git
work trees, therefore `git describe` won't ever have anything to
describe. Avoid related warnings, switch to BUILD_ID-based versioning
by default.

Fixes errors like:
  fatal: No tags can describe '<frameworks/base-commit>'.
  Try --always, or create some tags.
  fatal: No names found, cannot describe anything.

Issue: FP3-A11#181
Change-Id: I30d95ae28e1667ef01f1400ee886a2cd6da63571
1 file changed