GMP mercurial host blocks certain IP ranges about cheribuild

[jrtc27]

My recollection was that either such a git mirror didn’t exist or it was outdated back when I added gmp as a mercurial repo. Using git is certainly easier (the MercurialRepository implementation is quite crude and easy to break if you make local changes, but good enough for our use case) provided we know that we can rely on the mirror going forwards. There’s also the issue of needing to convert the user’s checkout from mercurial to git, which I don’t think needs to be any more complex than informing the user (in the same way as we do for switching branches) and then wiping the directory if it’s got a .hg subdirectory, as I highly doubt users have local changes (if they do they should save them elsewhere before saying yes to the prompt).

[qwattash]

I don't have anything against it. The commits appear to be in sync on the main branch.