Makefile.in: Fix errors introduced in previous change (in particular...

	* Makefile.in: Fix errors introduced in previous change (in particular,
	errors when building gnattools were ignored).
	Code clean up and simplification.
	update comments.
	Remove temporary debug code introduced by mistake in previous check in.
	Prefer GNU Make syntax over complex and error-prone sh syntax.
	(gnatlib-zcx): New target.
	(ada.all.cross): Merged with gnattools-cross target.

From-SVN: r80857