Porting issue in visual studio 2015 - _flag is not a member of _iobuf

Question

I am porting existing VC12 compiler compatible code to VC14 (visual studio 2015) and I am facing code break problem.

Sample program to reproduce issue:

#include "iostream"
using namespace std;
#define mybuffer(param)       ((param)->_flag & (_IOMYBUF))

int main()
{
    mybuffer(stderr); // I don't understand what is the purpose of this line.
                      // So, facing issue in replacing this code statement.
    return 0;
}

On visual studio 2013: above program works absolutely fine.

On visual studio 2015: above program gives compilation error.

Error C2039 '_flag': is not a member of '_iobuf'

Error C2065 '_IOMYBUF': undeclared identifier

Analysis:

In VS2013, wchar.h has following:

struct _iobuf {
    char *_ptr;
    int   _cnt;
    char *_base;
    int   _flag;
    int   _file;
    int   _charbuf;
    int   _bufsiz;
    char *_tmpfname;
    };
typedef struct _iobuf FILE;

Where as in VS2015, in file: corecrt_wstdio.h

#ifndef _FILE_DEFINED
#define _FILE_DEFINED
typedef struct _iobuf
{
    void* _Placeholder;
} FILE;
#endif

Can you please help me in suggesting a fix for above error?