I used meta-clang in my recipes and I noticed that: 1. The current release of poky uses LLVM v11.1.0 by default (poky/meta/recipes-devtools/llvm/llvm_git.bb) 2. Meta-clang requires LLVM v12.0.0 (meta-clang/conf/layer.conf defines LLVMVERSION = "12.0.0")
As a result just including meta-clang into bblayers.conf will require bitbake to build a new version of LLVM and rebuild everything which uses it