Basically fixing original Bug#427 reported by MArkus Elfring.
Unfortunately there are still more defines (in IrrCompileConfig.h) which also are not nice c++
Lots of files touched for very minor cleanup *sigh*
git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6253 dfc29bdd-3216-0410-991c-e03cc46cb475