Well, I'm not giving up yet, although some of you probably wish I would.  Sorry that my poorly-formed makefile caused such confusion.  For what it's worth I sincerely appreciate experts being willing to help out those of us who are new.  
 

You've satisfied your curiosity, on a side issue.  However, I suspect
that, by introducing this red herring, and dogmatically pounding on
about it, you may have left the OP, (and any number of less experienced
users), deeply confused, (if indeed, they didn't give up even trying to
follow the diversion, long ago).

BUT, from everything I've read in this thread I understand that a makefile with a single line as follows:

 graphictest: graphictest.o c:\GTK\include\gtk-2.0\gtk 

SHOULD work, yes?  The good news is that running it doesn't generate the "multiple target patterns" error but it does generate the "No such file or directory" error.  Now even I can figure out what that's supposed to mean, but the file I'm trying to include in my C program (#include <gtk.h>) IS in that directory.  Am I still doing something wrong here?