config.host: Allow unknown hosts (not targets).

config.host: Allow unknown hosts (not targets).

	* config.host: Allow unknown hosts (not targets).  Allow
	ns32k-*-netbsdelf* as a host (not a target).  Remove redundant
	empty clauses.  Remove useless obsolete-configuration clause.
	Prune unsupported configuration list.  Collapse identical
	clauses for closely related systems.  Rewrite comment for
	unsupported hosts list.  Reorganize a little.

From-SVN: r71686