Utilities/Sphinx: Add missing call to note_explicit_target

Sphinx calls document.note_explicit_target with any nodes.target() it
creates.  Add such a call when we create a document target in
CMakeTransform.

Utilities/Sphinx/cmake.py

@@ -203,6 +203,7 @@ class CMakeTransform(Transform):
             # Insert the object link target.
             targetid = '%s:%s' % (objtype, title)
             targetnode = nodes.target('', '', ids=[targetid])
+            self.document.note_explicit_target(targetnode)
             self.document.insert(0, targetnode)
             # Insert the object index entry.
             indexnode = addnodes.index()