result_of cannot handle member function pointer to __cdecl function

Might be a root cause of https://github.com/boostorg/phoenix/issues/81

```cpp
#include
#include

struct X
{
bool __cdecl f();
};

using F = decltype(&X::f);

using A = std::result_of::type; // fine
using B = boost::result_of::type; // fails
```

https://godbolt.org/z/WGMKezqd7

There should be much more of these calling convention stuff that will brakes result of, see https://github.com/boostorg/type_traits/blob/30396ed792697b5a5a7c4f02f7e22ae8d6ad95fd/include/boost/type_traits/detail/is_member_function_pointer_cxx_11.hpp