Update gcc_release for move to git.

This patch updates the gcc_release script, used for snapshots and
releases, to use git instead of SVN.

The parts of the changes used in building snapshots have been tested.
The parts used for building releases have not, so it's likely further
fixes may turn out to be needed there when releases are first built
from git.

	* gcc_release: Use git instead of SVN.
	* crontab: Update gcc_release calls.