Add some missing #if conditionals from Apple's code drop (#620) * arm/aarch64: Add FFI_CLOSURES conditionals where appropriate Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com> * aarch64: Don't emit the do_closure label when building without FFI_GO_CLOSURES Signed-off-by: Jeremy Huddleston Sequoia <jeremyhu@apple.com>