Comment 3 for bug 68459

The date portion of the UA was intended to be a "source" date, not a build date.
If it were generated as part of the *checkout* target it would not cause undue
extra linkage in layout.

On the plus side developer builds would have meaningful and consistent build
ID's. On the down side there might not be a way to distinguish official release
"re-spins". Does that happen often enough (without re-pulling) to matter?