[IRA] Fix PR91052 by skipping multiple_sets insn in combine_and_move_insns

[IRA] Fix PR91052 by skipping multiple_sets insn in combine_and_move_insns

As PR91052's comments show, commit r272731 exposed one issue in function
combine_and_move_insns.  Function combine_and_move_insns perform the
unexpected movement which alter live interval of some register, leading
incorrect value to be used.  See PR91052 for details.

2020-02-12  Kewen Lin  <linkw@gcc.gnu.org>
    PR target/91052
    * ira.c (combine_and_move_insns): Skip multiple_sets def_insn.