Implement N3421; comparison predicates<void>

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@187357 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/utilities/function.objects/comparisons/greater.pass.cpp b/test/utilities/function.objects/comparisons/greater.pass.cpp
index 2cadd6d..8e9a891 100644
--- a/test/utilities/function.objects/comparisons/greater.pass.cpp
+++ b/test/utilities/function.objects/comparisons/greater.pass.cpp
@@ -23,4 +23,15 @@
     assert(!f(36, 36));
     assert(f(36, 6));
     assert(!f(6, 36));
+#if _LIBCPP_STD_VER > 11
+    typedef std::greater<> F2;
+    const F2 f2 = F2();
+    assert(!f2(36, 36));
+    assert(f2(36, 6));
+    assert(!f2(6, 36));
+    assert( f2(36, 6.0));
+    assert( f2(36.0, 6));
+    assert(!f2(6, 36.0));
+    assert(!f2(6.0, 36));
+#endif
 }