Fix candidate for PR c++/43206

Fix candidate for PR c++/43206

gcc/cp/ChangeLog:
	PR c++/43206
	* cp-tree.h (get_template_parms_at_level): Declare ...
	* pt.c (get_template_parms_at_level): ... new function.
	* typeck.c (get_template_parms_of_dependent_type): If a template
	type parm's DECL_CONTEXT isn't yet set, get its siblings from
	current_template_parms. Use get_template_parms_at_level. Remove
	useless test.
	(incompatible_dependent_types_p): If we get empty parms from just one
	of the template type parms we are comparing then the template parms are
	incompatible.

gcc/testsuite/ChangeLog:
	PR c++/43206
	* g++.dg/template/typedef30.C: New test case.

From-SVN: r157730