re PR c++/66850 (Adding a forward declaration of a template containing a template template parm causes ICE on valid code)

Fix PR c++/66850

gcc/cp/ChangeLog:

	PR c++/66850
	* pt.c (redeclare_class_template): Set the DECL_CONTEXTs of each
	template template parm in the redeclaration.
	(lookup_template_class_1): Peel off irrelevant template levels
	from current_template_parms before augmenting the argument
	list.

gcc/testsuite/ChangeLog:

	PR c++/66850
	* g++.dg/template/pr66850.C: New test.

From-SVN: r225801