lra: consider clobbers when selecting hard_regno to spill

lra: consider clobbers when selecting hard_regno to spill

The idea behind the rclass loop in spill_hard_reg_in_range() seems to
be: find a hard_regno, which in general conflicts with reload regno,
but does not do so between `from` and `to`, and then do the live range
splitting based on this information. To check the absence of conflicts,
we make use of insn_bitmap, which does not contain insns which clobber
the hard_regno.

gcc/ChangeLog:

2018-07-30  Ilya Leoshkevich  <iii@linux.ibm.com>

        PR target/86547
	* lra-constraints.c (spill_hard_reg_in_range): When selecting the
	hard_regno, make sure no insn between `from` and `to` clobbers it.

From-SVN: r263063