c++: Use %qs in diagnostic message [PR93882]

A tweak for translators, as requested in the PR.

2020-02-22  Marek Polacek  <polacek@redhat.com>

	PR c++/93882
	* decl.c (grokdeclarator): Use %qs in a diagnostic message.

gcc/cp/ChangeLog

+2020-02-22  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/93882
+	* decl.c (grokdeclarator): Use %qs in a diagnostic message.
+
 2020-02-21  Martin Sebor  <msebor@redhat.com>
 
 	PR gcov-profile/93753

gcc/cp/decl.c

@@ -11251,7 +11251,7 @@ grokdeclarator (const cp_declarator *declarator,
   if (constinit_p && typedef_p)
     {
       error_at (declspecs->locations[ds_constinit],
-		"%<constinit%> cannot appear in a typedef declaration");
+		"%qs cannot appear in a typedef declaration", "constinit");
       return error_mark_node;
     }