MAKEALL: fix cross-compiler lookup breakage after CROSS cleanup

Commit ae14cd49a8da6e62e35636 broke testing of multiple arches in one go.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

extra/scripts/MAKEALL

@@ -127,6 +127,8 @@ for a in "$@" ; do
 	else
 		mark_arch pass $a
 	fi
+
+	unset CROSS_COMPILE
 done
 
 if [ -n "${skip}" ] ; then