Next to the text input box for Target Objects for constraints, I added a menu where one can select an existing object for the target. To see the menu, add a constraint such as ik solver. Then next to the box for the target name a box will also appear which opens up to a menu when clicked. Each time I added a constraint, I noticed it would be nice to have a menu to select existing objects rather than needing to remember the name of the object. All the needed modifications happened in "blender/source/blender/src/buttons_object.c".