Do not build GCC 4.2.1 by default for any CPU architecture

By default set to NO:

GCC
GCC_BOOTSTRAP
GNUCXX

As described by imp@ on the freebsd-arch mailing list Aug 13, 2019 with
Subject: Gcc 4.2.1 to be removed before FreeBSD 13, a firm timeline
https://lists.freebsd.org/pipermail/freebsd-arch/2019-August/019674.html

Reviewed by: jhb, imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D23026