[MarcZX10]

What

The relinker execution checks for --to-rosetta and AMD64-only conversions are compiled only for x86-64, but the existing macOS relinker matrix builds only the runner's native architecture. Add a macOS x86-64 matrix entry, install Rosetta, and pass CMAKE_OSX_ARCHITECTURES through CMake so those tests execute on Apple Silicon CI.

This is complementary to #3962, which adds x86-64 coverage for register-context and write-watch tests.

Tested

• On an M1 / macOS 26.6.2, the contributor ran the exact job configuration under Rosetta: x86-64 relinker and all 178/178 tests passed in 30 seconds; ANDN and AMD64-only execution checks ran. Native arm64 configuration remained 178/178 passing with the expected x86-64-only check skipped.
• python3 tools/check_conventions.py --base upstream/main passes.
• git diff --check upstream/main...HEAD passes.
• Patch overlap warnings for ci: run the macOS write watch and register context tests under Rosetta #3962, test: organize library tests and label CTest suites #6044 and ci(relinker): run TLS function coverage tests under ASan on Linux #7096 were reviewed manually; their edits are in separate workflow blocks. I could not run macOS or actionlint in this Linux environment; hosted CI has not reported checks yet.

Checklist

• Based on current main; no open PR implements the relinker x86-64 runner.
• One topic per PR; follow-ups go in a new PR.
• No comments added to code.
• No unimplemented paths added.
• No notes, investigation files or images added.
• No third-party code added.
• Generic CI coverage.
• Depends on: none.
• Fixes: relinker CI: build the macOS relinker for x86-64 so the Rosetta execution tests run #7188.
• Unblocks: none.
• GPUs tested: n/a.
• AI-assisted: yes.

[MarcZX10]

Closing this duplicate: the same #7188 change was already carried and submitted as PR #7197, with hosted macOS x86-64 relinker, register-context, and write-watch checks passing there. I missed that existing submission in the initial search. This PR adds no distinct behavior.