When trying to build libafl-libfuzzer with a custom `CARGO_TARGET_DIR`, the following call fails: https://github.com/AFLplusplus/LibAFL/blob/90cb9a2919faf386e0678870e52784070cdac4b6/crates/libafl_libfuzzer/build.rs#L163 Likely we'll have to calculate paths differntly in this case.