LLVM: upgrade to 19.1.4

• https://discourse.llvm.org/t/llvm-19-1-3-relased/82829
• https://discourse.llvm.org/t/llvm-19-1-4-released/83230

there's a (delayed) 19.1.4 release any time now https://discourse.llvm.org/t/llvm-19-1-4-release-update/83088

but I want to see if anything will fail here, and also again try to upgrade community/openmp