[llvm] [LLVM] Move `prepare-check-lit` dep to specialized testsuite (PR #159922)

[Michał Górny via llvm-commits]

mgorny wrote:

Unfortunately, that doesn't really change anything for us at all. While we're probably never going to run these "specialized" test suite, CMake will still fail over unsatisfiable dependencies.

https://github.com/llvm/llvm-project/pull/159922