[class.virtual] Add \grammarterm for using-declaration (cplusplus#9314)

Author: Andreas-Krug

source/classes.tex

@@ -3820,7 +3820,7 @@
 void foo() {
   C c;
   c.f();            // calls \tcode{B::f}, the final overrider
-  c.C::f();         // calls \tcode{A::f} because of the using-declaration
+  c.C::f();         // calls \tcode{A::f} because of the \grammarterm{using-declaration}
 }
 \end{codeblock}
 \end{example}