[llvm] Revert "[CI] Migrate to runtimes build" (PR #143612)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> If https://github.com/llvm/llvm-project/pull/143597 lands before I press 'squash and merge' here, happy to wait and see if that fixes forward

I doubt it will, but we'll see. I'm not super confident that's the right fix and want someone who actually understands the compiler-rt build to look it over.

https://github.com/llvm/llvm-project/pull/143612