ci: add linux-aarch64 to the libretro cross-compile early-warning gate

[doublegate]

Summary

Adds aarch64-unknown-linux-gnu to the libretro-cross early-warning gate in ci.yml, giving PR-time CI coverage to the Linux aarch64 cross-compile that #331 ships to the GitLab buildbot.

Why

#331 adds a libretro-build-linux-aarch64 job to .gitlab-ci.yml, but a GitHub PR can't run GitLab pipelines — so that cross-compile has no pre-merge signal here. The libretro-cross gate exists precisely to close that blind spot (it was added after buildbot pipeline #91899 failed 9/10 jobs on problems reproducible in seconds on a GH runner). This extends it to the target #331 introduces.

Why no per-target step is needed

• cargo check, not build: the gate never links, so ci: add a Linux aarch64 build #331's cross linker (aarch64-linux-gnu-gcc) and STRIP override — which only matter at link/package time — are irrelevant here.
• bindgen resolves libretro.h from clang's freestanding builtins: the header includes only stdint.h / stddef.h / limits.h / stdbool.h. Verified with cargo check --release -p rustynes-libretro --target aarch64-unknown-linux-gnu on a host with zero aarch64 system headers installed — the whole graph (cpu/ppu/apu/mappers/core/rust-libretro/rustynes-libretro, bindgen included) compiled clean in ~3 min. So, unlike Android's bionic (which needs the NDK sysroot), the generic rustup target add + cargo check steps cover it with no extra wiring.

Relationship to #331

Companion to #331 (Linux aarch64 buildbot job by @WizzardSK). That PR is the feature; this is the CI insurance that keeps the aarch64 cross-compile green on every PR going forward. Different files, independent — merge order doesn't matter.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Chores
  • Expanded cross-compilation coverage to include Linux on aarch64.
  • Added the required cross-compilation headers and configuration for generating bindings on the new target.
  • Improved build workflow documentation for platform-specific sysroot and header requirements.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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Run ID: 92f7a072-0886-43e1-9b88-2a1cafe2f28d

📥 Commits

Reviewing files that changed from the base of the PR and between 90c74c6 and d03f9b7.

📒 Files selected for processing (1)

• .github/workflows/ci.yml

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📝 Walkthrough

Walkthrough

The libretro-cross CI job now builds for aarch64-unknown-linux-gnu, installs the corresponding glibc cross headers, and configures bindgen with the AArch64 sysroot and include path.

Changes

Libretro AArch64 cross-build

Layer / File(s)	Summary
AArch64 target and bindgen provisioning .github/workflows/ci.yml	The matrix adds aarch64-unknown-linux-gnu; a conditional step installs gcc-aarch64-linux-gnu and exports bindgen sysroot/include arguments, with updated inline documentation.

Estimated code review effort: 2 (Simple) | ~10 minutes

Possibly related PRs

• doublegate/RustyNES#317: Updates the same workflow job with target-specific bindgen configuration for Android.
• doublegate/RustyNES#331: Adds a separate CI AArch64 cross-build path.

Suggested labels: bug

🚥 Pre-merge checks | ✅ 9

✅ Passed checks (9 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: adding linux-aarch64 coverage to the libretro cross-compile CI gate.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Docs-As-Spec Sync	✅ Passed	Only .github/workflows/ci.yml changed; no crates/rustynes-{cpu,ppu,apu,mappers} or matching docs files were touched, so no docs sync was needed.
Changelog Entry For User-Visible Changes	✅ Passed	Only .github/workflows/ci.yml changed; this is CI/tooling-only, and the Unreleased changelog section is intentionally empty.
No Unwrap/Expect/Panic On Untrusted Input	✅ Passed	Only .github/workflows/ci.yml changed; no Rust code paths or new unwrap/expect/panic sites touching untrusted inputs were added.
Safety Comment On New Unsafe Blocks	✅ Passed	PR only changes .github/workflows/ci.yml; no Rust source or new unsafe blocks/fns were added.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci/libretro-linux-aarch64-gate

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[github-actions]

Antigravity review (Gemini via Ultra)

This pull request adds aarch64-unknown-linux-gnu to the cargo check CI matrix in .github/workflows/ci.yml and installs ARM64 glibc headers so bindgen can parse target headers.

Blocking issues

None found.

Suggestions

• .github/workflows/ci.yml:424-425: Install libc6-dev-arm64-cross directly instead of gcc-aarch64-linux-gnu. The comment explicitly notes that the GCC cross-linker and binutils are unused for cargo check; installing only libc6-dev-arm64-cross with --no-install-recommends reduces CI package download overhead.

Nitpicks

• .github/workflows/ci.yml:424: Pass --no-install-recommends to apt-get install to avoid pulling unnecessary recommended packages into the CI environment.

_{Automated first-pass review by agy on a self-hosted runner -- not a human review.}