devel/ocaml-opam: Update to 2.2.1
Makefile is adjusted to use --with-vendored-deps for configure, and drop
the (cold-)lib-ext target that is not needed anymore.
Determine ARCH by bsd.port.pre.mk.
Add LICENSE_FILE.
Changelog: https://github.com/ocaml/opam/releases/tag/2.2.1
PR: 280227
Approved by: submitter is maintainer