c++: do_class_deduction and dependent init [PR93383]

c++: do_class_deduction and dependent init [PR93383]

Here we're crashing during CTAD with a dependent initializer (performed
from convert_template_argument) because one of the initializer's
elements has an empty TREE_TYPE, which ends up making resolve_args
unhappy.

Besides the case where we're initializing one template placeholder
from another, which is already specifically handled earlier in
do_class_deduction, it seems we can't in general correctly resolve a
template placeholder using a dependent initializer, so this patch makes
the function just punt until instantiation time instead.

gcc/cp/ChangeLog:

	PR c++/89565
	PR c++/93383
	PR c++/95291
	PR c++/99200
	PR c++/99683
	* pt.c (do_class_deduction): Punt if the initializer is
	type-dependent.

gcc/testsuite/ChangeLog:

	PR c++/89565
	PR c++/93383
	PR c++/95291
	PR c++/99200
	PR c++/99683
	* g++.dg/cpp2a/nontype-class39.C: Remove dg-ice directive.
	* g++.dg/cpp2a/nontype-class45.C: New test.
	* g++.dg/cpp2a/nontype-class46.C: New test.
	* g++.dg/cpp2a/nontype-class47.C: New test.
	* g++.dg/cpp2a/nontype-class48.C: New test.