src-ext: fix extlib url

[rjbou]

Seems that ygreg.org.ua is no more reachable and the package redirects to ygrek.org.

[MisterDA]

Why not switch to 1.7.7 and GitHub?
https://github.com/ygrek/ocaml-extlib/archive/1.7.7.tar.gz

[dra27]

Assuming it's still working, there's an update-sources script in src_ext which should try to pull the URLs for the latest versions of all the lib-ext and lib-pkg packages from opam… the only tedium then is updating the patches, if necessary.

[rjbou]

@MisterDA we rely on the package defined url.
@dra27 Thanks, I didn't saw the script, very helpful! I'm updating it to check that the package version is compliant with the 4.02.3 ocaml lower bound.
I'll merge this one to unlock the CI, and do another PR for the script update & version bump.

[rjbou]

related discussion #4097 & PR #4098

[dra27]

@rjbou - the script doesn't need to check that - the src_ext is meant to include patches to ensure 4.02.3 compatibility (if necessary). So after running the script, you then test make lib-ext and ensure that the patches work (usually, fortunately, it's a matter of deleting dune overlays). I'm just doing a PR for 4.09.1

[rjbou]

ok, perfect! Thanks!