Help/prop_sf/LABELS: link to the `LABELS` target property

Help/prop_sf/LABELS.rst

@@ -4,5 +4,5 @@ LABELS
 Specify a list of text labels associated with a source file.
 
 This property has meaning only when the source file is listed in a
-target whose ``LABELS`` property is also set.  No other semantics are
+target whose :prop_tgt:`LABELS` property is also set.  No other semantics are
 currently specified.