[codex] arm64e upstream-ready integration stack

[cypherair]

Summary

This is the fork-only integration/reference stack for the current arm64e upstream-ready PR set. It combines the contents of the three upstream-facing branches, a small integration-only visionOS+ptrauth cross-check follow-up, and a final CypherAir-only workflow commit for fork arm64e validation.

Included upstream-ready PRs:

• target: add arm64e-apple-visionos rust-lang/rust#155715: target: add arm64e-apple-visionos
• arm64e: set ptrauth ABI subtype on lib.rmeta Mach-O objects rust-lang/rust#155716: arm64e: add Apple pointer authentication codegen support
• bootstrap: handle fork shallow upstream detection rust-lang/rust#155717: bootstrap: handle fork shallow upstream detection

Integration-only follow-up:

• Adds visionOS revisions to the arm64e ptrauth codegen/UI diagnostic tests so the fork integration branch exercises the combined arm64e-visionOS+ptrauth surface.

The final .github/workflows/fork-arm64e.yml commit is fork-only and must not be included in any rust-lang/rust PR.

Validation before push

• git diff --check main...HEAD
• python3 x.py check compiler/rustc_codegen_ssa compiler/rustc_codegen_llvm --stage 1
• python3 x.py test --stage 1 --force-rerun on arm64e ptrauth codegen/assembly/UI tests plus tests/assembly-llvm/targets/targets-macho.rs
• python3 x.py build compiler/rustc library/std --stage 1 --target arm64e-apple-darwin
• python3 x.py test src/bootstrap --stage 1 --test-args 'test_push_ci test_ci_merge_without_upstream_parent_falls_back_to_nightly_ref'

Additional validation for the integration-only follow-up:

• git diff --check main...HEAD
• python3 x.py test --stage 1 --force-rerun tests/codegen-llvm/arm64e-apple-ptrauth.rs tests/codegen-llvm/arm64e-apple-ptrauth-calls.rs tests/codegen-llvm/arm64e-apple-ptrauth-fnptr-data.rs tests/codegen-llvm/arm64e-apple-ptrauth-invoke.rs tests/ui/compile-flags/invalid/branch-protection-arm64e-apple-pac-ret.rs tests/ui/compile-flags/invalid/target-feature-arm64e-apple-ptrauth-disable.rs

Notes

This supersedes the earlier integration PR #4 for ongoing fork validation. The previous PR #4 branch is retained for history until this replacement has a useful CI signal.

[cypherair]

Superseded by the new integration/arm64e-upstream-prs validation branch, which rebuilds the integration view from rust-lang/rust PRs rust-lang#155715, rust-lang#155716, and rust-lang#155717.