PR c++/77337 - auto return and lambda

PR c++/77337 - auto return and lambda

	* pt.c (tsubst_friend_function): Don't set DECL_INITIAL.
	(instantiate_decl): It's OK to defer a constexpr function.
	* cp-tree.h (DECL_FRIEND_PSEUDO_TEMPLATE_INSTANTIATION): Check
	DECL_LANG_SPECIFIC.
	* decl2.c (decl_defined_p): Use it.  No longer static.
	* decl.c (redeclaration_error_message): Use decl_defined_p.
	* constexpr.c (cxx_eval_call_expression): Set input_location around
	call to instantiate_decl.

From-SVN: r242056