utils/linkage: allow checking non-brew libraries

[cho-m]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew lgtm (style, typechecking and tests) with your changes locally?

---

This allows replacing some Homebrew/core system library checks where we are using Pathname#dynamically_linked_libraries (which will break if we stop monkey-patching Pathname).

For example

• https://github.com/Homebrew/homebrew-core/blob/c7150571f364c08554c028cb561e6871bb104636/Formula/z/zig.rb#L123-L124

The previous code skipped over non-Homebrew libraries and would always run realpath which is not guaranteed to exist for macOS system libraries.

---

This won't handle checking a symlinked system library. However, this feature isn't needed as it would only be used for Linux libraries but we already audit unwanted system library linkage.

If there is ever a case we want to check symlinked system library, could add an exist? check and then run realpath.

[Copilot]

Pull Request Overview

This PR enhances the Utils.binary_linked_to_library? method to support checking linkage to non-Homebrew (system) libraries, addressing a limitation in the previous implementation that only handled Homebrew libraries.

Key Changes:

• Modified the linkage checking logic to conditionally resolve symlinks only for Homebrew-prefix libraries
• Added support for checking non-Homebrew library linkage (e.g., system libraries in /usr/lib)
• Added test coverage for the new non-Homebrew library checking functionality

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
Library/Homebrew/utils/linkage.rb	Refactored binary_linked_to_library? to conditionally call File.realpath only for HOMEBREW_PREFIX paths, enabling non-brew library checks
Library/Homebrew/test/utils/linkage_spec.rb	Added test case to verify non-brew library linkage checking works correctly

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[MikeMcQuaid]

Looks good, thanks!