gcl 2.7.1 (new formula)

[cho-m]

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Using this for arm64 linux support for acl2.

Linux-only as doesn't build on arm64 macOS and we are deprecating Intel macOS.

[Copilot]

Pull Request Overview

This PR adds a new formula for GNU Common Lisp (GCL) version 2.7.1, a Common Lisp implementation. GCL is Linux-only and includes official errata patches plus a backported fix for Homebrew's non-lowercase CC path.

Key Changes:

• Adds GCL 2.7.1 formula with gmp and libtirpc dependencies
• Includes inline patches for official errata and Homebrew compatibility
• Provides basic test coverage for the Lisp interpreter

[github-actions]

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