cleaning up Microsoft Windows ifdef'ery

[Michael Stahl]

On 27.01.2016 14:33, Noel Grandin wrote:

> 15        _WIN32_WINNT_WINBLUE

this is actually a check of the SDK version to work around deprecation
warnings, so we need it as long as SDK 7.1 (and windows XP) are supported.

> 16        _WIN32_WINNT
> 27        _WIN64
> 5          _WINDOWS
> 1          _WINDOWS_
> 2          WNT

only 2? surely there are more?

> 2          XP_WIN

we also define WIN32, not sure why.