[committed] Make g++.dg/concepts/memfun-err.C compile-only

[Marek Polacek]

This test checks compile-time errors, so there's no point in trying to
actually run it.

Committed as obvious.

2018-10-22  Marek Polacek  <pola...@redhat.com>

        PR testsuite/87694
        * g++.dg/concepts/memfun-err.C: Make it a compile test.

--- gcc/testsuite/g++.dg/concepts/memfun-err.C
+++ gcc/testsuite/g++.dg/concepts/memfun-err.C
@@ -1,4 +1,4 @@
-// { dg-do run { target c++17 } }
+// { dg-do compile { target c++17 } }
 // { dg-options "-fconcepts" }