Always include sys/types.h from wx/filefn.h

It looks like the preprocessor checks were meant to avoid including this file
under MacOS 9 and all the other platforms should have it, so it should be safe
to include (although it still doesn't define off_t with MSVC, only _off_t).

include/wx/filefn.h

@@ -56,11 +56,7 @@
 #endif
 
 // define off_t
-#if !defined(__WXMAC__) || defined(__UNIX__) || defined(__MACH__)
-    #include  <sys/types.h>
-#else
-    typedef long off_t;
-#endif
+#include  <sys/types.h>
 
 #if defined(__VISUALC__)
     typedef _off_t off_t;