packaging: build libmpeg2 into macOS deps for CD32 FMV

packaging: build libmpeg2 into macOS deps for CD32 FMV

The DMG builds silently lost CD32 FMV video decode when Homebrew's
libmpeg2 moved to a macOS 26 baseline: the deployment-target check
rejects it against the 13.0 release target and no other copy exists.
Build libmpeg2 0.5.1 into the private deps prefix instead, pinned by
sha256 from the videolan tarball in CI. The 2008 tarball needs its
autotools regenerated to configure on arm64-apple-darwin and gnu89
inline semantics to link with clang, matching the Homebrew formula.