Update the compiler-rt patch (maybe this could be upstreamed, or try out
https://github.com/google/fuzztest?) and handle the ThreadPool ->
DefaultThreadPool rename.
Building on #3505, the toolchain and llvm rules require a little more
special-casing to get them to work well. This also moves
libprotobuffer_mutator, but that one's more minor. The migration
encounters more quirks in repo naming as seen by various queries.
This changes some of the toolchain work that was recently done for bazel
7 in #3496, dropping a bzl file I'd suggested to add, instead using
`:all` for toolchain registration. (somewhat as an improvement, somewhat
just to avoid a `load`)
Remaining in the WORKSPACE are example code repos and tree sitter rules.
Neither of these are part of the main toolchain builds, and so will
probably be lower impact if there's a good solution for them.
Jon Ross-Perkins