[PR87770] test partial specializations for type dependence

[PR87770] test partial specializations for type dependence

When instantiating a partial specialization of a template member
function for a full specialization of a class template, we test
whether the context of variables local to the partial specialization,
i.e., the partial specialization itself, is dependent, and this ICEs
in type_dependent_expression_p, when checking that the function type
isn't type-dependent because it is not in a type-dependent scope.

We shouldn't have got that far: the previous block in
type_dependent_expression_p catches cases in which the function itself
takes template arguments of its own, but it only did so for primary
templates, not for partial specializations.  This patch fixes that.

for  gcc/cp/ChangeLog

	PR c++/87770
	* pt.c (instantiates_primary_template_p): New.
	(type_dependent_expression_p): Use it.

for  gcc/testsuite/ChangeLog

	PR c++/87770
	* g++.dg/pr87770.C: New.

From-SVN: r268529