Building 32-bit RISC-V sysroots and images with Yocto

Thanks to the Debian 64-bit RISC-V port it's really easy to build a sysroot appropriate for cross-compiling Clang/LLVM and its separate test suite. Either use my rootless-deboostrap-wrapper script or the command I documented in LLVM's cross-compilation instructions, being sure to see the note on working around a Ninja dependency issue. For a bootable QEMU image, Debian-based recipes are similarly straightforward. But we don't have the luxury of a precompiled distribution for 32-bit RISC-V and so we'll lean on Yocto to produce the needed sysroot by building from source. I cover three cases: 1) building a sysroot for cross-compiling projects like LLVM, 2) doing the same but in a way that requires fewer build steps, 3) building an image approximating my debootstrap image recipes. In this article I use release 5.3 ('Whinlatter'), which introduced the bitbake-setup helper tool. For documentation, I found the Yocto quick build guide, and bitbake-setup docs, and image customisation guide…