macvim: remove reference to stray arch

Fixes #21925.
autoconf: force use of system perl

If a non-system perl is present when autoconf is built and subsequently
removed, autoconf will break. Force the use of the system perl to
prevent this.
automake: force use of system perl

If a non-system perl is present when automake is built and subsequently
removed, automake will break. Force the use of the system perl to
prevent this.