[llvm] Revert "Reapply "[CI] Migrate to runtimes build"" (PR #145742)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

I don’t really understand how this fixes it. The error is with clang-tools-extra which was built before this patch too. This patch just changes the runtime builds shouldn’t impact the check-clang-tools target.

I would also prefer to avoid reverting this if possible. The tight interaction between clang and libcxx made this a pain to land and to reland (three libcxx patches and one LWG issue required).

https://github.com/llvm/llvm-project/pull/145742