selinux: move BUILD_SELINUX_POLICY definition
BUILD_SELINUX_POLICY needs to be defined outside of ENABLE_SERVER
conditional block.
Fixes:
\# ./configure --disable-server
...
configure: error: conditional "BUILD_SELINUX_POLICY" was never defined.
Usually this means the macro was only invoked conditionally.
Reviewed-By: Christian Heimes <cheimes@redhat.com>