[llvm] [LLVM] Remove explicit dependency on builtins build (PR #159854)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

I'm not sure separating the steps will help unless I'm missing something. The builtins and runtimes builds are part of the same build target as far as I know. The fundamental problem occurs because we cannot do proper dependency management between this barrier. Normally you'd have the runtimes depend on the builtins, but because of the BUILD_ALWAYS usage this is always out of date. You can get rid of `BUILD_ALWAYS` but then there's no way to inform the top level CMake that the dependencies are stale.

https://github.com/llvm/llvm-project/pull/159854