Find the native FLTK includes and library

By default FindFLTK.cmake will search for all of the FLTK components and add them to the FLTK_LIBRARIES variable.

You can limit the components which get placed in FLTK_LIBRARIES by
defining one or more of the following three options:
FLTK_SKIP_OPENGL, set to true to disable searching for opengl and
                  the FLTK GL library
FLTK_SKIP_FORMS, set to true to disable searching for fltk_forms
FLTK_SKIP_IMAGES, set to true to disable searching for fltk_images
FLTK_SKIP_FLUID, set to true if the fluid binary need not be present
                 at build time

The following variables will be defined:

FLTK_FOUND, True if all components not skipped were found
FLTK_INCLUDE_DIR, where to find include files
FLTK_LIBRARIES, list of fltk libraries you should link against
FLTK_FLUID_EXECUTABLE, where to find the Fluid tool
FLTK_WRAP_UI, This enables the FLTK_WRAP_UI command

The following cache variables are assigned but should not be used. See the FLTK_LIBRARIES variable instead.

FLTK_BASE_LIBRARY   = the full path to fltk.lib
FLTK_GL_LIBRARY     = the full path to fltk_gl.lib
FLTK_FORMS_LIBRARY  = the full path to fltk_forms.lib
FLTK_IMAGES_LIBRARY = the full path to fltk_images.lib