The Fast Light Tool Kit ("FLTK", pronounced "fulltick") is a
a cross-platform C++ GUI toolkit for UNIX(r)/Linux(r) (X11),
Microsoft(r) Windows(r), and MacOS(r) X. FLTK provides modern GUI
functionality without the bloat and supports 3D graphics via OpenGL(r)
and its built-in GLUT emulation. It was originally developed by
Mr. Bill Spitzak and is currently maintained by a small group of
developers across the world with a central repository in the US.

If you want to disable cairo support, you need to pass CAIRO=0 to the
build script.