Add an osinclude.h below each OS directory, redirects by platform macro

* Linux folder has been renamed to Unix, to match defines and so that it
  compiles on OS X.
* This removes the need for a per-platform include search path for the
  right OS folder

StandAlone/Worklist.h

@@ -35,7 +35,7 @@
 #ifndef WORKLIST_H_INCLUDED
 #define WORKLIST_H_INCLUDED
 
-#include "osinclude.h"
+#include "../glslang/OSDependent/osinclude.h"
 #include <string>
 #include <list>