rtl-optimization/104686 - speed up conflict iteration

rtl-optimization/104686 - speed up conflict iteration

The following replaces

       /* Skip bits that are zero.  */
       for (; (word & 1) == 0; word >>= 1)
         bit_num++;

idioms in ira-int.h in the attempt to speedup update_conflict_hard_regno_costs
which we're bound on in PR104686.  The trick is to use ctz_hwi here
which should pay off even with dense bitmaps on architectures that
have HW support for this.

For the PR in question this speeds up compile-time from 31s to 24s for
me.

2022-02-25  Richard Biener  <rguenther@suse.de>

	PR rtl-optimization/104686
	* ira-int.h (minmax_set_iter_cond): Use ctz_hwi to elide loop
	skipping bits that are zero.
	(ira_object_conflict_iter_cond): Likewise.