Allow varying ranges of unknown types in irange::verify_range [PR109711]

Allow varying ranges of unknown types in irange::verify_range [PR109711]

The old legacy code allowed building ranges of unknown types so passes
like IPA could build and propagate VARYING.  For now it's easiest to
allow the old behavior, it's not like you can do anything with these
ranges except build them and copy them.

Eventually we should convert all users of set_varying() to use
supported types.  I will address this in my upcoming IPA work.

	PR tree-optimization/109711

gcc/ChangeLog:

	* value-range.cc (irange::verify_range): Allow types of
	error_mark_node.