Consider me a newbie.  I had used xdu long long ago, and decided to try to compile xdiskusage for my new machine (which is running RH Linux 2.6.32-279.2.1.el6.x86_64.)  I compiled fltk, or thought I did, successfully - apparently it passes its own demo/test.   Then when I run make, after autoconf and configure, I get 

$ make
g++  -o xdiskusage panels.o xdiskusage.o  -lfltk -lXinerama -lGL -lGLU -lX11 -lXext  -lm
/usr/local/lib/libfltk.a(fl_font.o): In function `Fl_Xlib_Graphics_Driver::width(unsigned int)':
fl_font.cxx:(.text+0x19d): undefined reference to `XftTextExtents32'
/usr/local/lib/libfltk.a(fl_font.o): In function `Fl_Xlib_Graphics_Driver::rtl_draw(char const*, int, int, int)':
fl_font.cxx:(.text+0x216): undefined reference to `FcUtf8Len'
fl_font.cxx:(.text+0x266): undefined reference to `FcUtf8ToUcs4'

So it appears not to be finding the fltk stuff, maybe?   Any suggestions about what I might do to debug this would be sincerely appreciated.

Thanks -