C++ PATCH to add test for c++/56428

[Marek Polacek]

Fixed by r215409.  The test is nice, so I'm adding it.

Tested on x86_64-linux, applying to trunk.

2019-08-02  Marek Polacek  <pola...@redhat.com>

        PR c++/56428
        * g++.dg/cpp0x/nontype4.C: New test.

diff --git gcc/testsuite/g++.dg/cpp0x/nontype4.C 
gcc/testsuite/g++.dg/cpp0x/nontype4.C
new file mode 100644
index 00000000000..2c552d00293
--- /dev/null
+++ gcc/testsuite/g++.dg/cpp0x/nontype4.C
@@ -0,0 +1,25 @@
+// PR c++/56428
+// { dg-do compile { target c++11 } }
+
+struct A { };
+
+template<bool B>
+  struct Builder
+  {
+    static A build() { return A(); }
+  };
+
+template<A (*F)()>
+  A f()
+  {
+    return Builder<F != nullptr>::build();
+  }
+
+A g();
+
+int main()
+{
+  f< &g >();
+  f< nullptr >();
+  f< &f<nullptr> >();
+}