[llvm] update `llvm.spec` (PR #65452)

[via llvm-commits]

pawosm-arm wrote:

There's something really disturbing about this file: it refers the `configure` script which is no longer part of LLVM. I suppose this file can be removed entirely. I'd suggest adding Tom Stellard and Sylvestre Ledru as reviewers as they can give you more definite answer whether this file is still needed.

https://github.com/llvm/llvm-project/pull/65452