The code needs to be cleaned up a little more. But it seems to work properly and is the preferred solution according to MSDN. Both solutions will be kept in the code, the choice define will be moved to IrrCompileConfig later.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@3705 dfc29bdd-3216-0410-991c-e03cc46cb475