lang_input_statement_type next pointers

lang_input_statement_type next pointers

"next" and "next_real_file" in lang_input_statement_type always point
to another lang_input_statement_type, so it makes sense for these to
not be the generic lang_statement_union_type.  This patch also updates
a number of variables in ldlang.c for the same reason, and modifies
lang_statement_append to reduce the need for casts.

	* ldlang.h (lang_input_statement_type): Make next
	and next_real_file a lang_input_statement_type pointer.
	(lang_statement_append): Delete prototype.
	(LANG_FOR_EACH_INPUT_STATEMENT): Update for lang_input_statement_type
	change.
	* ldmain.c (add_archive_element): Likewise.
	* ldlang.c: Likewise throughout.
	(lang_statement_append): Make static.  Make element and field
	void pointers.  Remove casts in calls.
	(lang_check): Use a lang_input_statement_type pointer for "file".
	(find_rescan_insertion): Similarly for "iter" and return value.
	(lang_process): Similarly for "insert", "iter" and "temp".
	* emultempl/spuelf.em (embedded_spu_file): Likewise.
	* emultempl/aix.em (gld${EMULATION_NAME}_before_allocation): Expand
	lang_statment_append call.