Building openmp using LLVM_ENABLE_RUNTIMES

I believe the difference between cmake’s LLVM_ENABLE_PROJECTS and LLVM_ENABLE_RUNTIMES is the latter uses the just-built clang to build the library.

That would be great for building the deviceRTL libraries and potentially good for testing builds of libomptarget while changing clang. Setting the cmake flag isn’t sufficient though:


That doesn’t print the usual output from configuring openmp and then doesn’t build it. I’ve been scattering ‘message’ through the CMakeLists trying to guess why not and have exhausted my shallow knowledge of how our build scripts work.

Can anyone hazard a guess at how to get this working?