untangle configuration of OpenGL, FLTK, and Qt (bug #47263) * configure.ac: Disentangle checks for FLTK, Qt, OpenGL, freetype, fontconfig, etc. * configure.ac (AMCOND_BUILD_QT_GRAPHICS): New automake conditional. * libgui/graphics/module.mk: Use it. * configure.ac (AMCOND_BUILD_QT_GUI): Rename from AMCOND_BUILD_GUI. Change all uses. (HAVE_OCTAVE_QT_GUI): Rename from HAVE_OCTAVE_GUI. Change all uses. * octave-gui.cc: Only initialize qt graphics toolkit if it is available. * __init_fltk__.cc: Only initialize fltk graphics toolkit if it is available. Allow compilation to succeed if FTLk widgets are availble but OpenGL is not. * __osmesa_print__.cc: Build even if OpenGL is not available. * acinclude.m4 (OCTAVE_CHECK_LIB_OPENGL): Move AC_DEFINE for HAVE_OPENGL here. * libinterp/link-deps.mk (LIBOCTINTERP_LINK_DEPS): Include $(FONTCONFIG_LIBS) and $(FREETYPE_LIBS) in the list.

--- a/libgui/module.mk	Sun Feb 28 20:58:56 2016 -0500
+++ b/libgui/module.mk	Sun Feb 28 23:03:54 2016 -0500
@@ -1,4 +1,4 @@
-if AMCOND_BUILD_GUI
+if AMCOND_BUILD_QT_GUI
 
 libgui_EXTRA_DIST =