staging: usbip: userspace: add option to turn fortify on or off

This comes handy when hacking with different cross
compilers, some of which may or may not have
_FORTIFY_SOURCE turned on by default. This patch
allows us to turn _FORTIFY_SOURCE on by specifying
--with-fortify option at configuration time (or
to turn it off by specifying --without-fortify).

If nothing is specified, default compiler behavior
is assumed.

Signed-off-by: Ilija Hadzic <ihadzic@research.bell-labs.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>