We don't use fltk_images or fltk_forms, so don't try to detect those (otherwise,...

We don't use fltk_images or fltk_forms, so don't try to detect those (otherwise, when linking against libfltk.a, the build system will try to link with libfltk_images.a and libfltk_forms.a as well, which can introduce external dependencies that we don't want.)

git-svn-id: svn://svn.code.sf.net/p/tigervnc/code/trunk@4521 3789f03b-4d11-0410-bbf8-ca57d06f2519