be01f42f73
The new pass manager is enabled by default in clang since Clang/LLVM 13. While the discussion about this is still ongoing (https://lists.llvm.org/pipermail/llvm-dev/2021-August/152305.html) it's expected that support for the legacy pass manager will be dropped either in LLVM 14 or 15. This switches us to use the new pass manager if LLVM >= 13 is used.