ocaml 5

[David Holland <dholland-pkgtech%netbsd.org@localhost>]

I have updated ocaml to 4.12.2 (this should probably have been done
some time back, it's purely maintenance fixes) but it's definitely
time we should move to ocaml 5 after the branch.

I will take charge of this (jaapb can't) so if anyone knows of
anything that will definitely need to be updated first (besides Coq,
which I'm already aware of), let me know. Or post here.

-- 
David A. Holland
dholland%netbsd.org@localhost