The Makefile only compiles this module if it is enabled.
I think it's better to error out if for some reason this doesn't work instead
of silently producing an empty modperl.so.
git-svn-id: https://znc.svn.sourceforge.net/svnroot/znc/trunk@1165 726aef4b-f618-498e-8847-2d620e286838