package/macos: use a different minimal macOS version depending on arch

arm64 macOS started at 11.0¹. We don't need to force disabling code always available on arm64 builds (via -Werror=partial-availability).

The compiler even tags the objects with macOS 11 even when using -mmacosx-version-min=10.11

main.c.o was built for newer 'macOS' version (11.0) than being linked (10.11)

1. https://en.wikipedia.org/wiki/MacOS_version_history#Overview ↩