The status badge should report the most recent status for the master
branch, not the most recent actions run.
llvm.sh wasn't updated when trunk moved to 14 so was failing to fetch clang-13 (which is now in the llvm-toolchain-focal-13 repo, not the llvm-toolchain-focal repo). Duplicate the correct logic here rather than relying on the external script.
A few highlights relative to our existing CI:
- Add a FreeBSD 12.2 and 13.0 runner so we have some FreeBSD CI.
- Windows builds use msbuild with the Visual-Studio-provided clang toolchain to test clang
- The matrix builds describe the axes of the matrix, not all points.
- The Arm builds now cross-compile with a native clang and run the tests with qemu, rather than running the compiler, linker, and ctest all with qemu.
This also includes a fix for one of the tests that was doing `static_cast<unsigned int>(1) << 36`, which is undefined behaviour and was sometimes causing qemu to hang. There is now an assert to catch this in the future.
