Simplify build configuration

- Use ubuntu-24.04 runner so we get a more recent clang version
- Use native arm64 build, getting rid of zig
- Remove setup steps for dependencies that are already installed on the runner
  images
- CLANG_ENABLE_ARCMT is deprecated, don't attempt to disable it
- Fix thinLTO support

Merge pull request #14 from cloudflare/gbedford/matrix-fail-fast-false

Don't fail-fast the LLVM build matrix

Merge pull request #14 from cloudflare/gbedford/matrix-fail-fast-false

Don't fail-fast the LLVM build matrix

Merge pull request #14 from cloudflare/gbedford/matrix-fail-fast-false

Don't fail-fast the LLVM build matrix

Merge pull request #14 from cloudflare/gbedford/matrix-fail-fast-false

Don't fail-fast the LLVM build matrix

Merge pull request #14 from cloudflare/gbedford/matrix-fail-fast-false

Don't fail-fast the LLVM build matrix

Merge pull request #14 from cloudflare/gbedford/matrix-fail-fast-false

Don't fail-fast the LLVM build matrix

Merge pull request #14 from cloudflare/gbedford/matrix-fail-fast-false

Don't fail-fast the LLVM build matrix

Merge pull request #14 from cloudflare/gbedford/matrix-fail-fast-false

Don't fail-fast the LLVM build matrix

Merge pull request #14 from cloudflare/gbedford/matrix-fail-fast-false

Don't fail-fast the LLVM build matrix