c++: Diagnose earlier non-static data members with cv containing class type [PR116108]

c++: Diagnose earlier non-static data members with cv containing class type [PR116108]

In r10-6457 aka PR92593 fix a check has been added to reject
earlier non-static data members with current_class_type in templates,
as the deduction then can result in endless recursion in reshape_init.
It fixed the
template <class T>
struct S { S s = 1; };
S t{2};
crashes, but as the following testcase shows, didn't catch when there
are cv qualifiers on the non-static data member.

Fixed by using TYPE_MAIN_VARIANT.

2024-12-17  Jakub Jelinek  <jakub@redhat.com>

	PR c++/116108
gcc/cp/
	* decl.cc (grokdeclarator): Pass TYYPE_MAIN_VARIANT (type)
	rather than type to same_type_p when checking if the non-static
	data member doesn't have current class type.
gcc/testsuite/
	* g++.dg/cpp1z/class-deduction117.C: New test.