[llvm] [openmp] Deprecate LLVM_ENABLE_PROJECTS in favor of LLVM_ENABLE_RUNTIMES (PR #124711)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> I believe this comes from Fortran module (`.mod`) files being compiler dependent. But they are also an integral part of the compiler. So, if `flang` wants to allow `use omp_lib` then it needs to have the OpenMP `.mod` file compiled. But it can/should/must (?) only do so when OpenMP is actually enabled. I'm not saying that the way this is currently done is great, just trying to give a bit of context. @Meinersbur can likely correct me if I'm wrong.

I figured it was just like `clang` which put those in the resource directory.

https://github.com/llvm/llvm-project/pull/124711