Fix inheriting constructor test for std::function.

The test I originally checked in only worked with ToT Clang. This patch
updates the test so that it works as far back as 3.5.



git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@276093 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/function.objects/func.wrap/func.wrap.func/derive_from.pass.cpp

@@ -7,6 +7,8 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++98, c++03
+
 // <functional>
 
 // See https://llvm.org/bugs/show_bug.cgi?id=20002
@@ -15,9 +17,10 @@
 #include <type_traits>
 
 using Fn = std::function<void()>;
-struct S : Fn { using function::function; };
+struct S : public std::function<void()> { using function::function; };
 
 int main() {
-    S f1( Fn{} );
+    S s( [](){} );
-    S f2(std::allocator_arg, std::allocator<void>{}, Fn{});
+    S f1( s );
-}
+    S f2(std::allocator_arg, std::allocator<int>{}, s);
+}