c++: ICE with auto[] and VLA [PR102414]

c++: ICE with auto[] and VLA [PR102414]

Here we ICE in unify_array_domain when we're trying to deduce the type
of an array, as in

  auto(*p)[i] = (int(*)[i])0;

but unify_array_domain doesn't arbitrarily complex bounds.  Another
test is, e.g.,

  auto (*b)[0/0] = &a;

where the type of the array is

  <<< Unknown tree: template_type_parm >>>[0:(sizetype) ((ssizetype) (0 / 0) - 1)]

It seems to me that we need not handle these.

	PR c++/102414
	PR c++/101874

gcc/cp/ChangeLog:

	* decl.cc (create_array_type_for_decl): Use template_placeholder_p.
	Sorry on a variable-length array of auto.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp23/auto-array3.C: New test.
	* g++.dg/cpp23/auto-array4.C: New test.