linkage_checker: always report incorrect :no_linkage

[cho-m]

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:no_linkage only makes sense if there is actually no linkage. There shouldn't be any false positives here (though the linkage may differ on macOS/Linux which is possible to handle via on_system blocks).

Just helps improve the metadata. Won't have a functional impact even if incorrect :no_linkage as we don't use this data outside of brew linkage output. But helps keep a canonical representation of a formula.

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Among remaining that are strict-only:

• Missing RPATH has a lot of false positives as shared modules/bundle (macOS .so files) usually don't use dyld but we still report those.
• @executable_path are usually app bundles. This could be a potential issue when an app bundle includes copies of libraries, but we sometimes fix these up via symlinks so can be a false positive. Not sure if we can guarantee no usage of this.

For declared deps, I think that will fail the test if a dependency is linked into library but not installed during test. Though I can't tell if there are any false positives here so will leave this strict-only.

[Copilot]

Pull request overview

This PR adjusts LinkageChecker so that formulas declaring dependencies as :no_linkage are always reported (and treated as failures in --test mode) when linkage is actually present, rather than only surfacing this under --strict.

Changes:

• Always display “Unexpected linkage for no_linkage dependencies” in display_test_output, regardless of strict.
• Treat @unexpected_linkage_deps as a --test failure condition even when strict: false.

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[MikeMcQuaid]

Good idea, thanks!