Version reporting: Restart active use of revision.h, now based on a git tag.

Version reporting: Restart active use of revision.h, now based on a git tag.

The new make-revision script regenerates glslang/Include/revision.h,
used as it always has been, but made with a git-tag version and the
the number of commits on master.

I have a pre-commit hook that will automatically do this on master,
likely often enough to work in practice, without needing pull requests
to include it.