You make it sound simple. Bazel's docs are minimal and what exists is often wrong. For a C or C++ toolchain you might turn to a contributing project such as toolchains_llvm, but even those experts are still figuring it out, and they give you little guidance on how to assemble your sysroot, which is the actual issue in the article. And, the upstream distributions of LLVM are built under certain assumptions, so unless you know exactly what you are doing, you probably also want to build LLVM instead of using their archives. If you figure out how to build LLVM in a completely consistent and correct way with respect to the STL and support libraries, you will be perhaps the 3rd or 4th person in history to achieve it.