scons: s/HAVE_NO_AUTOCONF/HAVE_SCONS/

Back when autotools and scons were the two build systems, it kinda made
sense to call scons "not autoconf", but autoconf's been gone for a while
now and other build systems have been added (android.mk and meson), so
the name really doesn't make any sense anymore.

Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
10 jobs for !1210 with autoconf-scons
merge request