Suppress diagnostics substituting into a requires-expression (PR c++/92403).

gcc/cp/
	* pt.c (tsubst_copy_and_build): Perform the first substitution without
	diagnostics and a second only if tsubst_requries_expr returns an error.

From-SVN: r278449

gcc/cp/ChangeLog

+2019-11-19  Andrew Sutton  <asutton@lock3software.com>
+
+	PR c++/92403
+	Suppress diagnostics substituting into a requires-expression.
+	* pt.c (tsubst_copy_and_build): Perform the first substitution without
+	diagnostics and a second only if tsubst_requries_expr returns an error.
+
 2019-11-19  Jakub Jelinek  <jakub@redhat.com>
 
 	PR c++/92504

gcc/cp/pt.c

@@ -20139,7 +20139,12 @@ tsubst_copy_and_build (tree t,
       }
 
     case REQUIRES_EXPR:
-      RETURN (tsubst_requires_expr (t, args, complain, in_decl));
+      {
+	tree r = tsubst_requires_expr (t, args, tf_none, in_decl);
+	if (r == error_mark_node && (complain & tf_error))
+	  tsubst_requires_expr (t, args, complain, in_decl);
+	RETURN (r);
+      }
 
     case RANGE_EXPR:
       /* No need to substitute further, a RANGE_EXPR will always be built