build-sys: must link with -fstack-protector

It is needed to give that flag to the linker as well, but latest
libtool 2.4.2 still swallows that argument, so let's pass it with
libtool -Wc argument.

qemu-1.4.0/stubs/arch-query-cpu-def.c:6: undefined reference to `__stack_chk_guard'

Signed-off-by: Marc-André Lureau <mlureau@redhat.com>
Reviewed-by: Alon Levy <alevy@redhat.com>
