re PR c++/43558 (Rejects specialization)

Fix PR c++/43558

gcc/cp/ChangeLog:
	PR c++/43558
	* cp-tree.h (TEMPLATE_TYPE_PARM_SIBLING_PARMS): New accessor macro.
	* pt.c (end_template_parm_list): Store sibling template parms of
	each TEMPLATE_TYPE_PARMs into its TEMPLATE_TYPE_PARM_SIBLING_PARMS.
	(push_template_decl_real): Don't store the containing template decl
	into the DECL_CONTEXT of TEMPLATE_TYPE_PARMs anymore.
	* typeck.c (get_template_parms_of_dependent_type): Get sibling parms
	of a TEMPLATE_TYPE_PARM from TEMPLATE_TYPE_PARM_SIBLING_PARMS.
	Simplify the logic.

gcc/testsuite/ChangeLog:
	PR c++/43558
	* g++.dg/template/typedef31.C: New test.

From-SVN: r157857