[llvm] [llvm][CMake] Introduce LLVM_RUNTIME_<project>_BUILD in CMake (PR #88934)

[Louis Dionne via llvm-commits]

https://github.com/ldionne commented:

I'm not sure about this approach.

It seems to me that you should instead have a parameter you pass to lit with `--param` and then have it set from the CI cache you use to configure your build. That would prevent having to infer whether a project is being built or not.

The reason why I'm lukewarm about this change is that it adds yet another procedural aspect to our CMake builds, and we've been working hard to get rid of that. We want to move towards more declarative (and more modern) CMake constructs where we define targets and avoid global state and logic, and this basically introduces another way to add such logic. So while I don't 100% understand your use case and the constraints you have to solve it, this specific approach seems like the wrong one to me at a high level.

https://github.com/llvm/llvm-project/pull/88934