[libclc] [llvm] [polly] [llvm] Move sub-project lead maintainers into their own Maintainers.md files (PR #118309)

[Tobias Grosser via llvm-commits]

tobiasgrosser wrote:

Sure, this works for me. Thank you @Meinersbur for all your work here. I am happy to help out if this is useful.

https://github.com/llvm/llvm-project/pull/118309