Add a target hook for assembling undeclared decls.

Add a target hook for assembling undeclared decls.

	* target.def (assemble_undefined_decl): New hooks.
	* hooks.c (hook_void_FILEptr_constcharptr_const_tree): New function.
	* hooks.h (hook_void_FILEptr_constcharptr_const_tree): Declare.
	* doc/tm.texi.in (TARGET_ASM_ASSEMBLE_UNDEFINED_DECL): Add.
	* doc/tm.texi: Regenerate.
	* output.h (assemble_undefined_decl): Declare.
	(get_fnname_from_decl): Declare.
	* varasm.c (assemble_undefined_decl): New function.
	(get_fnname_from_decl): New function.
	* final.c (rest_of_handle_final): Use it.
	* varpool.c (varpool_output_variables): Call assemble_undefined_decl
	for nodes without a definition.

From-SVN: r217293