finally found it:
By default on windows the c++ compilers are not installed by installing visualstudio community 2015.
After installing visualstudio community 2015 you can install the c++ SDK by trying to open an own softwareobject. Do this:
You need to launch Visual studio, then do: file > new > project, in the window than opened, select "Model > Visual C++" and in the middle of the window you should see a button "install microsoft C++" or something like that, click on it and it will launch the install process for the C++ & Microsoft SDK.
Be ready to watch your machine again installing for half an hour, eating another GB. Of course i get the incompatibilitywarning again:
But who cares? Ican build my own megaglrst64.dev again, enjoing being blocked from lobby!
There might be some installation-properties you can set at first installing of "visualstudio community 2015" to avoid this fumbling around. Maybe someone checks that out and put it to the compiling WIKI.
Dont expect Windowsusers to do researches like this. There is a reason, why they are not at Linux.