syoyo/llvm-project-mingw-build ? reverse-engineered prompt

Build me a simple set of shell scripts that can set up and build llvm project for a MinGW Windows target using llvm mingw on Linux.

I want to be able to clone the llvm project repo, build the needed native tools first, then build the Windows cross compiled pieces like libclang and libllvm, and also have a separate script for building libcxx, libcxxabi, and compiler rt. It should be easy to edit the path to the llvm mingw toolchain in one place and then run the scripts from the command line.

Please make it work in a way that matches a typical Ubuntu build flow, with clear steps in the README for what to install and how to run everything. If anything needs current setup details from upstream llvm or llvm mingw, look them up online and use the latest sensible approach. Also include a basic GitHub Actions workflow so the build can run in CI and produce artifacts or release outputs later.