Revert from backup of main GMP repo

[Torbjörn Granlund]

I've reverted the main gmp repository /var/hg/gmp from backup in order
to resolve broad breakage.  The public mirror will be auto-synched soon.

I don't think a repo which has been synchronised with /var/hg/gmp since
2020-11-15 will work properly.

For those of you that have a checkout locally which you have synched
with the main repository since or during 2020-11-15, you might also want
to restore from /home/.zfs/snapshot/2020-11-15.

Please re-commit tested changes to the restored /var/hg/gmp which got
reverted as a result of my action.

-- 
Torbjörn
Please encrypt, key id 0xC8601622