There are four ports in the way of removing llvm/18 from the tree:

devel/rust-bindgen	only tdep -> update to 0.72.0 on ports@

devel/c2ffi		no official llvm/18 support, doesn't link with 19

devel/woboq_codebrowser	probably needs some patching

lang/crystal		should support 19 already

It would be nice if we could fix these soon.