scons/windows: Enable compute shaders when possible.

Tests done with llvm-config indicate that there are only 2 libraries in
irreader and not in engine, LLVMAsmParser and LLVMIRReader and both of them
are part of coroutines so I replaced irreader with coroutines and added
libraries unique to coroutines.
40 jobs for !2162 with windows-compute-shaders in 19 minutes and 43 seconds (queued for 3 seconds)
merge request