FreeBSD 11: Don't use imported x11/motif, use installed versions for build

With this patch, the import symlinks for x11 and motif do not need to
be created.  The build will use the installed headers in
/usr/local/include/{X11, Xm}.

This will work for FreeBSD 11 only ATM as I don't have older systems
to test with.

It may work for FreeBSD 10 or earlier versions as well.  If so, edit
config/cf/FreeBSD.cf and change the OSMajorVersion check for
UseInstalledX11 appropriately.  And send a patch to the CDE mailing
list :)

cde/config/cf/FreeBSD.cf

@@ -73,6 +73,12 @@ USE_GCC = UseGcc
 # define HasGcc2		YES
 #endif
 
+/* Use installed X11 includes/libs on FreeBSD 11+ */
+#if (OSMajorVersion >= 11)
+#define UseInstalledX11         YES
+#endif
+
+
 /* For DtHelp TIFF processing routines. */
 #ifdef AMD64Architecture
 #define LSBBitOrder             YES