OpenBSD 6+: use installed X11 and Motif

This commit removes the need to setup X11 and motif import symlinks
before building CDE.  With OpenBSD v6+, the installed versions of X11 and
Motif will be used.

This may work with earlier versions of OpenBSD as well, but I don't
have access to those older versions.  If you try it, and it works,
send a patch to the CDE mailing list.

This was tested on OpenBSD 6.2

cde/config/cf/OpenBSD.cf

@@ -148,6 +148,11 @@ XCOMM operating system:  OSName (OSMajorVersion./**/OSMinorVersion./**/OSTeenyVe
 # endif
 #endif
 
+/* Use installed versions of Xm and X11 */
+#if OSMajorVersion >= 6
+# define UseInstalledX11        YES
+#endif
+
 /*
  * Compiler Features
  */