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

OGLCompilersDLL/InitializeDll.h

@@ -35,7 +35,7 @@
 #define __INITIALIZEDLL_H
 
 
-#include "osinclude.h"
+#include "../glslang/OSDependent/osinclude.h"
 
 namespace glslang {