zstd support

[jmhodges]

The next release of LLVM, 22.1.8, will have zstd artifacts attached to the build.

See llvm/llvm-project#164537

Those files will be smaller in size. It would be nice for toolchains_llvm to support using those zstd tarballs.

(Also, thanks so much for your work)

[AustinSchuh]

It works today, though it is not the most integrated. We've been building our own artifacts and using them for a while for all the reasons listed out.

llvm = use_extension("@toolchains_llvm//toolchain/extensions:llvm.bzl", "llvm", dev_dependency = True)

llvm_version = "21.1.8"

llvm_alternative_sources = [
    "https://github.com/RealtimeRoboticsGroup/toolchains/releases/download/{llvm_version}/{basename}",
]

llvm_x86_64_basename = "clang+llvm-%s-x86_64-linux-gnu-ubuntu-22.04.tar.zst" % llvm_version

llvm_aarch64_basename = "clang+llvm-%s-aarch64-linux-gnu.tar.zst" % llvm_version

llvm_darwin_aarch64_basename = "clang+llvm-%s-aarch64-apple-darwin.tar.zst" % llvm_version

llvm_extra_distributions = {
    llvm_x86_64_basename: "3e9ab559182f45143c36d761fcee6818935187a8f54354ecb043643b642769f0",
    llvm_aarch64_basename: "68172a4b557ab3ae50fcc27d3e706d066ea5891933e50f6fb97d6ca9f7e2beb4",
    llvm_darwin_aarch64_basename: "b2fcfe47b336cc48077f2c9b98e5636bbdf89f17dd6596908dec5a2cb5c87de9",
}

llvm.toolchain(
    name = "llvm_k8",
    alternative_llvm_sources = llvm_alternative_sources,
    distribution = llvm_x86_64_basename,
    extra_llvm_distributions = llvm_extra_distributions,
    # MemorySanitizer-instrumented libc++ overlay, swapped in for builds with
    # `--features=msan` (see `build:msan` in .bazelrc). Same LLVM version as the
    # base toolchain so it is ABI-compatible with clang 21.1.8.
    libcxx_sha256 = "56e33981bb71aba8704026534093f81ba9783cff0bf701681f1781d2ecb50a87",
    libcxx_url = "https://github.com/RealtimeRoboticsGroup/toolchains/releases/download/21.1.8/libcxx-msan-21.1.8-x86_64-linux-gnu-ubuntu-22.04.tar.zst",
    llvm_versions = {"": llvm_version},
)