fixed cpp warning due to missing #ifdef directive in lib/util/debug.h

[github at samba.org]

New comment by abartlet on Samba Github repository

https://github.com/samba-team/samba/pull/51#issuecomment-446877763
Comment:
My apologies for the very long delay in dealing with this. 

I really don't think this patch is right.  If DEBUG is already defined, then why not all the others.  My guess is an unrelated DEBUG with a different meaning is defined in this build environment. 

Either way, our web-based development tooling has moved to GitLab, so we are clearing out the old Pull Requests here. 

Sorry,

Andrew Bartlett