Skip compute-runtime fetch

I am currently trying to build llvm on NixOS, so I can package dpc++ for nixpkgs. To do so, I need to prefetch everything, and it is not allowed to fetch it otherwise by other means (due to it not being 100% reproducible). I usually fix things setup by setup, but I am stuck now at this line: https://github.com/oneapi-src/unified-runtime/blob/6f36300dbf36d80b12d103c1e06243c5f7bd9776/cmake/FetchLevelZero.cmake#L111

Usually, it is possible to specify the source directory of a dependency, like UR_LEVEL_ZERO_LOADER_LIBRARY, which is an option in the same file. This isn't the case for the compute-runtime, which seems to be fetched from GitHub. Is there a possibility of skipping this using a CMake option?

My only other option is to make a patch and delete those lines, which is usually a last resort.

If someone is interested, here is my nix file for creating the derivation for building dpcpp so far.

Start at cmake/FetchLevelZero.cmake around line 111 and compare the compute-runtime fetch with the UR_LEVEL_ZERO_LOADER_LIBRARY option in the same file. Review the linked dpcpp/default.nix derivation to understand the prefetch constraint; done means a CMake configuration can use a pre-fetched compute-runtime without fetching from GitHub.