IssueTracker

Presently, we've authored a large BUILD.gn file (third_party/llvm-10/BUILD.gn) that manually brings in a (somewhat) minimal set of source files to build for SwiftShader. This has been difficult to author correctly as there are so many GN builds for many targest and configurations. Furthermore, when upgrading LLVM to a newer version, we sometimes need to update this list to include new files, or remove/rename files.

LLVM now offers unofficial support for GN builds. See this: https://github.com/llvm/llvm-project/tree/master/llvm/utils/gn

What we can do is keep our root BUILD.gn file, but have it add dependencies on only the required libs out of utils/gn/secondary/llvm/lib/. To make this work, we'll need to modify our third_party/update-llvm-10.sh to have it add /llvm/utils/gn to the sparse-checkout of llvm so that it gets copied to our third_party/llvm-10/llvm.