[polly] [polly] Create component and install target in add_polly_library (PR #66598)

[Sam James via llvm-commits]

thesamesam wrote:

@Meinersbur could you take a look? It looks fine to me but I'm not one of the polly maintainers. The CMake part of polly doesn't seem to have any particular maintainer so I'd consider just merging it myself anyway but I figured I'd ask.

https://github.com/llvm/llvm-project/pull/66598