DtSvc/dtwm: Fix some implicit declarations of functions by adding appropriate

Patch from Frederic Koehler <f.koehler427@gmail.com>:

These implicit definitions cause segfaults on x64 because
the implicit return type is a 32-bit signed int, rather than a pointer
type.

cde/programs/dtwm/WmWrkspace.c

@@ -41,6 +41,7 @@ static char rcsid[] = "$XConsortium: WmWrkspace.c /main/7 1996/10/23 17:26:33 rs
 #include "WmGlobal.h"
 #include "WmHelp.h"
 #include "WmResNames.h"
+#include "WmIPlace.h"
 #include <X11/Xutil.h>
 #include "WmICCC.h"
 #include <Xm/Xm.h>