(scan_loop): Correct comment.

(strength_reduce): Correct comments.  Don't set maybe_multiple when
pass branch to scan_start.  Don't set not_every_iteration after
passing a CODE_LABEL, or after passing a branch out of the loop.
When outputting DEST_ADDR giv increments, put them next to the memory
address on machines with auto-increment addresses.
(record_biv): Set new field always_executed.
(record_giv): Set new fields always_executed and auto_inc_opt.
(maybe_eliminate_biv_1): Reject biv with auto_inc_opt optimization
in some cases.

From-SVN: r11090