ci: streamline release builds on GitHub-hosted runners

[yanghang8612]

Summary

• disable test targets and build only the release compiler target on native platforms
• migrate Windows, macOS, Linux AMD64, Linux ARM64, and Emscripten builds to GitHub-hosted runners
• pin the Windows runner to windows-2022
• pin macOS to macos-15, Xcode 16.4, CMake 3.29.3, and a cached universal Boost 1.84 build
• run Linux AMD64 and Emscripten builds on ubuntu-24.04 and Linux ARM64 on ubuntu-24.04-arm
• transfer build outputs with Actions artifacts and gather them on the self-hosted Linux runner
• keep only the S3 packaging/upload job on [self-hosted, Linux]

Why

The release workflow only consumes solc and soljson, so compiling test executables and auxiliary targets wastes build time. The platform builds no longer need persistent self-hosted machines once their dependencies and toolchains are prepared explicitly.

The S3 job remains self-hosted to preserve the existing production credentials and bucket-access environment.

Impact

• Windows builds solc.exe with TESTS=OFF on windows-2022.
• macOS builds the existing x86_64 + arm64 universal solc on macos-15.
• Linux AMD64 and ARM64 build their static solc binaries on native GitHub runners.
• Emscripten continues to build only soljson.
• Artifact executable bits are restored before packaging on Linux.
• The packaging job extracts the version from the Linux AMD64 binary instead of trying to run the macOS binary on Linux.

Validation

• actionlint passed for .github/workflows/build.yml
• YAML runner graph, submodule checkout, and artifact upload/download pairing checks passed
• git diff --check passed
• bash -n passed for the Unix and Emscripten build scripts
• prior hosted-runner migration run passed Windows, macOS universal, macOS Intel-slice execution, Linux static, Emscripten, and release-format packaging: https://github.com/yanghang8612/solidity/actions/runs/29404474021
• prior Windows TESTS=OFF + solc-only benchmark and binary smoke test passed: https://github.com/yanghang8612/solidity/actions/runs/29407834749

The fork did not expose the production S3 secrets during the migration rehearsal. The S3 upload path remains on the repository's self-hosted Linux runner and will be exercised by the production workflow after merge.

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