Summary: This PR primarily changes using `LLVM_RUNTIMES_TARGET` to `LLVM_DEFAULT_TARGET_TRIPLE`. The reason is that the default target triple is the true cross-compiling architecture we are using, while the runtimes_target can contain multilib strings like `+debug` or similar. Additionally add the proper path handling to the OpenMP / Offload libraries.
See docs/CMake.html for instructions on how to build LLVM with CMake.