Preserve relative path names in $srcdir. Build symlink tree if
configuring cross target dir and srcdir=. (= no VPATH support).
(configure-target-libg++): Depend on configure-target-librx.
* cfg-ml-com.in, cfg-ml-pos.in: Deleted.
* config-ml.in: New file.
* symlink-tree: New file.
* configure: Ensure srcdir="." if that's what it is.
