GL should not be a completely necessary thing for finding GTK. This will find gtk and GL but also just GTK

Modules/FindGTK.cmake

@@ -109,10 +109,8 @@ IF (UNIX)
   IF(GTK_gtk_INCLUDE_PATH)
   IF(GTK_glibconfig_INCLUDE_PATH)
   IF(GTK_glib_INCLUDE_PATH)
-  IF(GTK_gtkgl_INCLUDE_PATH)
   IF(GTK_gtk_LIBRARY)
   IF(GTK_glib_LIBRARY)
-  IF(GTK_gtkgl_LIBRARY)
 
     # Assume that if gtk and glib were found, the other
     # supporting libraries have also been found.
@@ -120,27 +118,36 @@ IF (UNIX)
     SET( GTK_FOUND "YES" )
     SET( GTK_INCLUDE_DIR  ${GTK_gtk_INCLUDE_PATH}
                            ${GTK_glibconfig_INCLUDE_PATH}
-                           ${GTK_glib_INCLUDE_PATH}
-                           ${GTK_gtkgl_INCLUDE_PATH} )
-    SET( GTK_LIBRARIES  ${GTK_gtkgl_LIBRARY}
-                        ${GTK_gtk_LIBRARY}
+                           ${GTK_glib_INCLUDE_PATH} )
+    SET( GTK_LIBRARIES  ${GTK_gtk_LIBRARY}
                         ${GTK_gdk_LIBRARY}
                         ${GTK_gmodule_LIBRARY}
+                        ${GTK_glib_LIBRARY} )
+
+  IF(GTK_gtkgl_INCLUDE_PATH)
+  IF(GTK_gtkgl_LIBRARY)
+    SET( GTK_GL_FOUND "YES" )
+    SET( GTK_INCLUDE_DIR  ${GTK_INCLUDE_DIR}
+                           ${GTK_gtkgl_INCLUDE_PATH} )
+    SET( GTK_LIBRARIES  ${GTK_LIBRARIES}
                         ${GTK_glib_LIBRARY}    )
 
+    MARK_AS_ADVANCED(
+      GTK_gtkgl_LIBRARY
+      GTK_gtkgl_INCLUDE_PATH
+      )
   ENDIF(GTK_gtkgl_LIBRARY)
+  ENDIF(GTK_gtkgl_INCLUDE_PATH)
+
   ENDIF(GTK_glib_LIBRARY)
   ENDIF(GTK_gtk_LIBRARY)
-  ENDIF(GTK_gtkgl_INCLUDE_PATH)
   ENDIF(GTK_glibconfig_INCLUDE_PATH)
   ENDIF(GTK_glib_INCLUDE_PATH)
   ENDIF(GTK_gtk_INCLUDE_PATH)
 
   MARK_AS_ADVANCED(
-    GTK_gtkgl_LIBRARY
     GTK_glib_LIBRARY
     GTK_gtk_LIBRARY
-    GTK_gtkgl_INCLUDE_PATH
     GTK_glibconfig_INCLUDE_PATH
     GTK_glib_INCLUDE_PATH
     GTK_gtk_INCLUDE_PATH