[over.match.class.deduct] Clarify that an incomplete class type is never

treated as being an aggregate.

Author: zygoloid

source/overloading.tex

@@ -1548,7 +1548,8 @@
 of the \grammarterm{deduction-guide}.
 \end{itemize}
 \end{itemize}
-In addition, if \tcode{C} satisfies the conditions for an aggregate class
+In addition, if \tcode{C} is defined
+and its definition satisfies the conditions for an aggregate class
 with the assumption that any dependent base class has
 no virtual functions and no virtual base classes, and
 the initializer is a non-empty \grammarterm{braced-init-list} or