re PR c++/70449 (ICE with -Wall on valid code on x86_64-linux-gnu in pp_string, at pretty-print.c:928)

	PR c++/70449

	PR c++/70344
	* pt.c (instantiate_decl): A function isn't fully defined if
	DECL_INITIAL is error_mark_node.
	* constexpr.c (cxx_eval_call_expression): Likewise.

From-SVN: r234695