sliming down devel/llvm11

In an effort to reduce build times a little prior to devel/llvm20
coming in the next month or so I took a look at devel/llvm11.  AFACT
there isn't a good path to remove it entierly due to dependencies in
lang/ghc810 and lang/ghc92 (at least on armv7 and maybe aarch64).  For
now I've put together a set of patches to remove other references to
it in ports and in the USES framework and then slim it down to just
building the LLVM core which is what I think GHC needs.

Those patches are at https://github.com/freebsd/freebsd-ports/pull/337

I've CC'd maintainers of everything I've touched.  I'm willing to submit
them another way if that is prefered, but this rolls them all up in one
place and most are trivial.  Please let me know what you'd like me to do
about the various patches.

Thanks,
Brooks