c++: var tmpl w/ dependent constrained auto type [PR103341]

c++: var tmpl w/ dependent constrained auto type [PR103341]

When deducing the type of a variable template (or templated static data
member) with a constrained auto type, we might need its template
arguments for satisfaction since the constraint could depend on them.

	PR c++/103341

gcc/cp/ChangeLog:

	* decl.c (cp_finish_decl): Pass the template arguments of a
	variable template specialization or a templated static data
	member to do_auto_deduction when the auto is constrained.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-class4.C: New test.
	* g++.dg/cpp2a/concepts-var-templ2.C: New test.

(cherry picked from commit e272cf95ba048fde60b21aee046c9ca9c9264425)