LLVM > 15

[fabianbs96]

We should upgrade PhASAR's required maximum LLVM version to something >15 to profit from API improvements and for compatibility with other tools, e.g., the IR used in rustc.

We should start with upgrading LLVM to 16.

Prerequisites:

• With LLVM 16, our clone of LLVM's CFLAndersAnalysis does not work anymore. We should either fix or replace it,

[fabianbs96]

Edit: We can quite easily fix the compilation issues in LLVM's CFLAndersAnalysis.

Checkout branch f-UpdateLLVM16 for the current dev version