The ‘core-updates’ branch has finally been merged.

It upgrades libc to 2.20, which fixes two security issues found in 2.19,
and fixes a bug in GCC 4.8.3.

Now that hydra.gnu.org is in better shape, I hope it will be easier to
deploy such fixes in the future.  However, we must also be diligent in
not triggering full rebuilds for unrelated issues when the deployment of
security fixes is at stake.  (I plead guilty.)

Ludo’.