Makefile.in: Revert most of Arnaud's last change.

	* Makefile.in: Revert most of Arnaud's last change.  Prefer anything
	over error-prone Make abuse.  Remove temporary debug code.
	(gnatlib-zcx): New target.
	(gnattools): Split into gnattools-native, gnattools-cross, to fix
	previous bug; select which on the basis of default_gnattools_target.
	(ada.all.cross): Merged with gnattools-cross target.
	* configure.ac: Set default_gnattools_target.
	* configure: Regenerate.

From-SVN: r81128