[libcxx] LWG2420 bits for bind<void> - Patch from K-Ballo

Implemented LWG2420 bits for bind<void>

Review: http://reviews.llvm.org/D10997


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@241967 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/utilities/function.objects/bind/func.bind/func.bind.bind/invoke_void_0.pass.cpp

@@ -39,21 +39,34 @@ test_const(const F& f)
 
 void f() {++count;}
 
-struct A_int_0
+int g() {++count; return 0;}
+
+struct A_void_0
 {
     void operator()() {++count;}
     void operator()() const {count += 2;}
 };
 
+struct A_int_0
+{
+    int operator()() {++count; return 4;}
+    int operator()() const {count += 2; return 5;}
+};
+
 int main()
 {
     test(std::bind(f));
     test(std::bind(&f));
-    test(std::bind(A_int_0()));
-    test_const(std::bind(A_int_0()));
+    test(std::bind(A_void_0()));
+    test_const(std::bind(A_void_0()));
 
     test(std::bind<void>(f));
     test(std::bind<void>(&f));
+    test(std::bind<void>(A_void_0()));
+    test_const(std::bind<void>(A_void_0()));
+
+    test(std::bind<void>(g));
+    test(std::bind<void>(&g));
     test(std::bind<void>(A_int_0()));
     test_const(std::bind<void>(A_int_0()));
 }