c++: Fix SEGV with malformed constructor decl.

c++: Fix SEGV with malformed constructor decl.

In the testcase, since there's no declaration of T, ref_view(T) declares a
non-static data member T of type ref_view, the same type as its enclosing
class.  Then when we try to do C++20 aggregate class template argument
deduction we recursively try to adjust the braced-init-list to match the
template class definition until we run out of stack.

Fixed by rejecting the template data member.

	PR c++/92593
	* decl.c (grokdeclarator): Reject field of current class type even
	in a template.