bb-reorder: Add -freorder-blocks-algorithm= and wire it up

bb-reorder: Add -freorder-blocks-algorithm= and wire it up

This adds an -freorder-blocks-algorithm=[simple|stc] flag, with "simple"
as default.  For -O2 and up (except -Os) it is switched to "stc" instead.
Targets that never want STC can override this.  This changes -freorder-blocks
to be on at -O1 and up (was -O2 and up).

In effect, the changes are for -O1 (which now gets "simple" instead of
nothing), -Os (which now gets "simple" instead of "stc", since STC results
in much bigger code), and for targets that wish to never use STC (not in
this patch though).

2015-09-23   Segher Boessenkool  <segher@kernel.crashing.org>

	* bb-reorder.c (reorder_basic_blocks): Use the algorithm selected
	with flag_reorder_blocks_algorithm.
	* common.opt (freorder-blocks-algorithm=): New flag.
	(reorder_blocks_algorithm): New enum.
	* flag-types.h (reorder_blocks_algorithm): New enum.
	* opts.c (default_options_table): Use -freorder-blocks at -O1 and up,
	and -freorder-blocks-algorithm=stc at -O2 and up (not at -Os).

From-SVN: r228318