Add Apple Silicon / arm64-compatible n64 formula and optional local sources

[JackTriton]

Add Apple Silicon-compatible n64 formula and optional local sources

This PR updates the Homebrew formulae for Apple Silicon while preserving the standard online installation workflow.

Before this, this PR is needed to be merged:

• Add Apple Silicon support and optional local toolchain sources glankk/n64#32

Changes

• Keep the official installation path:

  • ootrandomizer/tap/n64
  • ootrandomizer/tap/armips

• Add optional local source support through:

  • HOMEBREW_N64_SOURCE_DIR
  • HOMEBREW_N64_HEAD_URL
  • HOMEBREW_ARMIPS_SOURCE_DIR
  • HOMEBREW_ARMIPS_HEAD_URL

• Detect the installed versioned Homebrew GCC executable instead of relying on a fixed GCC version.

• Add GNU sed as a build dependency.

• Propagate GMP, MPFR, and MPC paths through the complete toolchain build.

• Use a serial build by default on Apple Silicon to improve reliability.

• Disable GDB and simulator components by default only on Apple Silicon, where the selected GDB and binutils releases may have incompatible internal APIs.

• Allow GDB and job count overrides through:

  • HOMEBREW_N64_BUILD_GDB
  • HOMEBREW_N64_JOBS

• Preserve the existing behavior on Intel macOS and other supported Homebrew platforms.

The default installation continues to use the configured online Git sources. Local directories are used only when explicitly requested.

[flagrama]

Disable GDB and simulator components by default only on Apple Silicon, where the selected GDB and binutils releases may have incompatible internal APIs.

This is not Apple Silicon related.