fix: make macOS release builds work on Apple Silicon (#258)

Before this change, the macOS release job failed on the arm64 runner:

```
  clang: error: include path for libstdc++ headers not found
  [-Werror,-Wstdlibcxx-not-found]
```

After this change, we unblock release jobs: release-mac builds for the
host architecture instead, so that macOS release artifacts are genuinely
arm64 (as the README and gem names claim, despite previously incorrectly
being x86_64 binaries.) toolchains_llvm is patched with a backport of
upstream PR 686 (released in v1.7.0) that drops `-L<toolchain>/lib` on
macOS; we can remove this patch when we upgrade later.

Verified locally on arm64: `release-mac` and `dev` builds of `//main:scip-ruby`
succeed, the release binary is arm64 with only system dylib deps, and
`//gems/scip-ruby` produces both `arm64-darwin` gems.

Signed-off-by: Emi <emi@sourcegraph.com>

fix: Stale check in publish script

chore: Prepare for v0.4.6 release (#236)

chore: Prepare for v0.4.5 release (#233)

chore: Fix lint errors in GitHub workflows (#230)

docs: Prepare for v0.4.3 release (#227)

docs: Prepare for v0.4.2 release (#224)

docs: Prepare for v0.4.1 release (#221)

ci: Use different names for build logs

docs: Add CHANGELOG entry for v0.3.9 (#206)