re PR c++/27640 (segfault, related to constructor instantiation and virtual base case and templates and new operator)

	PR c++/27640
	* pt.c (instantiate_template): Set processing_template_decl to
	zero while performing substitutions.
	PR c++/27640
	* g++.dg/template/ctor7.C: New test.

From-SVN: r114701