dealing with ports that need a root build

[David Thiel]

I'm working on updating the the submitted Samhain port to 1.7.4,
and trying to resolve a problem in the old one where the port has
to be built as root.  If the option --with-kcheck is enabled, part
of the build will require root privileges to read from /dev/mem.
I've disabled this option by default, but wanted to do something
like:

.if defined(WITH_KCHECK)
.if (check to see if user is root)
CONFIGURE_ARGS+=  --with-kcheck
.else echo "blah blah, be root to do this"
.endif
.endif

What's the proper way to do this?

Thanks,
david