configure script issue - looks for libxmu but doesn't detect libxmu6

When attempting configure and make for an XFCE4 based system, (this one is Zorin 16 Lite) the configure script looks for the "libxmu" library and tools, version 1.1.2+, but newer XFCE4 based systems often use "libxmu6", which is not detected. In fact the required libraries are available and of version 1.1.3.