devel/llvm-{cheri,morello}: new snapshots

Update CHERI and Morello LLVM compilers to new snapshots.

Attempt to fix builds with LLVM 21 by conditionally applying the patch
used with devel/llvm17. I'm not applying it universally as llvm-morello
fails to compile with it on my 14.4-RELEASE test system.

Sponsored by: DARPA, AFRL