[SFN] adjust RTL insn-walking API

This patch removes unused RTL functions, introduces alternate ones for
use in a later SFN patch, and regroups other related functions so that
they appear in a more consistent order.

for  gcc/ChangeLog

	* emit-rtl.c (next_nondebug_insn, prev_nondebug_insn): Reorder.
	(next_nonnote_nondebug_insn, prev_nonnote_nondebug_insn): Reorder.
	(next_nonnote_nondebug_insn_bb): New.
	(prev_nonnote_nondebug_insn_bb): New.
	(prev_nonnote_insn_bb, next_nonnote_insn_bb): Remove.
	* rtl.h	(prev_nonnote_insn_bb, next_nonnote_insn_bb): Remove decls.
	(prev_nonnote_nondebug_insn_bb): Declare.
	(next_nonnote_nondebug_insn_bb): Declare.
	* cfgbuild.c (find_bb_boundaries): Adjust to skip debug insns.
	* cfgrtl.c (get_last_bb_insn): Likewise.
	* lra.c (push_insns): Likewise.

From-SVN: r255564