More MSVC fixes
More MSVC fixes

* The custom spawn didn't need to be a class

* Use the custom spawn for MSVC too

* Filter away output from MSVC binaries that I don't seem to be able to
  get rid.

* Tuned warning options for MSVC so "--debug" is workable

* Working fallback to MinGW if MSVC is not in PATH environment, Scons
  doesn't seem to do that.

tempbottle/Nuitka,wfxiang08/Nuitka,kayhayen/Nuitka,kayhayen/Nuitka,kayhayen/Nuitka,tempbottle/Nuitka,tempbottle/Nuitka,wfxiang08/Nuitka,tempbottle/Nuitka,wfxiang08/Nuitka,kayhayen/Nuitka,wfxiang08/Nuitka