c++: Fix pasto in structured binding diagnostics [PR94571]

This snippet has been copied from the non-structured binding declaration
parsing later in the function, and while for non-structured bindings
it can be followed by comma or semicolon, structured bindings may be
only followed by semicolon.

Or, do we want to have a different message for the case when there is
a comma (and keep this corrected one only if there is something else)
that would explain better what is the bug (or add a fix-it hint)?
Marek said in the PR that clang++ reports
error: decomposition declaration must be the only declaration in its group

There is another thing Marek noted (though, something for different spot),
that diagnostic for auto x(1), [e,f] = test2; could also use a clearer
wording like the above (or a fix-it hint), but the question is if we should
assume [ after , as a structured binding or if we should do some tentative
parsing first to figure out if it looks like a structured binding.

2020-04-16  Jakub Jelinek  <jakub@redhat.com>

	PR c++/94571
	* parser.c (cp_parser_simple_declaration): Fix up a pasto in
	diagnostics.

	* g++.dg/cpp1z/decomp51.C: New test.

gcc/cp/ChangeLog

+2020-04-16  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/94571
+	* parser.c (cp_parser_simple_declaration): Fix up a pasto in
+	diagnostics.
+
 2020-04-15  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c/94593

gcc/cp/parser.c

@@ -13675,7 +13675,7 @@ cp_parser_simple_declaration (cp_parser* parser,
 	    if ((decl != error_mark_node
 		 && DECL_INITIAL (decl) != error_mark_node)
 		|| cp_parser_uncommitted_to_tentative_parse_p (parser))
-	      cp_parser_error (parser, "expected %<,%> or %<;%>");
+	      cp_parser_error (parser, "expected %<;%>");
 	    /* Skip tokens until we reach the end of the statement.  */
 	    cp_parser_skip_to_end_of_statement (parser);
 	    /* If the next token is now a `;', consume it.  */

gcc/testsuite/ChangeLog

+2020-04-16  Jakub Jelinek  <jakub@redhat.com>
+
+	PR c++/94571
+	* g++.dg/cpp1z/decomp51.C: New test.
+
 2020-04-15  Uroš Bizjak  <ubizjak@gmail.com>
 
 	PR target/94603

gcc/testsuite/g++.dg/cpp1z/decomp51.C

+// PR c++/94571
+// { dg-do compile { target c++17 } }
+
+void
+foo ()
+{
+  int e[2], f[2];
+  auto [a,b] = e, [c,d] = f;	// { dg-error "expected ';' before ',' token" }
+}
+
+void
+bar ()
+{
+  int e[2];
+  auto [a, b] = e );		// { dg-error "expected ';' before '\\\)' token" }
+}