Package gdk was not found in the pkg-config search path

[TomF <TomF sjpc org>]

On a Redhat 8.0 sytem, I ran pkg-config --list-all.  At the end of the
list, the following messages were displayed:

Package gdk was not found in the pkg-config search path.
Perhaps you should add the directory containing `gdk.pc'
to the PKG_CONFIG_PATH environment variable
Package 'gdk', required by 'ImlibGdk', not found

I could not find a gdk package or gdk.pc on my system or on the Redhat
distribution CDs, and I could not understand what I found in Google. 
However, gdk-pixbuf-xlib-2.0 and gdk-x11-2.0 are on my system.

What should I do to get rid of this message?