_WIN32 doesn’t mean what you think it does. It means “I am using the Windows API”. The 32 postfix was added back in the days of Windows NT 3.1 to make it distinct from the 16-bit API that was used in Windows version 3. This term has fallen out of favor because of the bitness problem. You can see this at stackoverflow.com, the [win32] tag takes you to [winapi].
Don’t remove it, you are using the Windows API.