Re: lang/rust: resurrect PORT_LLVM as a non-default OPTION

Hi Mark, yes it seems that some maintainers are letting dependencies
bloat.  A few weeks ago I had to rebuild samba4.13 (on FBSD 12.4) and it
required rust to build(!).  This was due to a documentation requirement to
use py-poetry .  Fortunately the py-poetry maintainer (I think) realised
and adjusted things within a week (Thanks).  More recently while building
security/py-cryptography I had to remove from the Makefile
${PYTHON_PKGNAMEPREFIX}setuptools-rust>=0.11.4:devel/py-setuptools-rust@${PY_FLAVOR}
[#1]
and comment out lines starting with CARGO (for obvious relationship reasons)

I don't use anything that requires rust but for some reason developers
don't provide a choice... so I've branched /usr/ports to track this
practice and retain reasonable build times.  Point?  Its not just docs that
you'll need to accommodate. :/

A better solution would be for maintainers to provide a choice to include
such monsters.
Cheers.
[#1] Refer
https://cgit.freebsd.org/ports/commit/?id=82c675ccaa87127ca291de1d224aa18cb782149f