fixes build issue for clang-3.2 and later (missing variable declaration in combination with -Werror causes build failure)
Fixes a build issue on pre-10.x FreeBSD systems, where MK_CTF is not defined (by /usr/share/mk/bsd.own.mk) yet.

The default on 9.1 and 10-CURRENT as of now is that CTF information is not used. With this patch, if MK_CTF is
undefined, the same logic as for MK_CTF == "no" will be employed.