Fix PR c++/42824

gcc/cp/ChangeLog:
	PR c++/42824
	* pt.c (lookup_template_class): Better support of specialization
	of member of class template implicit instantiation.

gcc/testsuite/ChangeLog:
	PR c++/42824
	* g++.dg/template/memclass4.C: New test.

From-SVN: r156939