PR rtl-optimization/40101

    PR rtl-optimization/40101
        * sel-sched-ir.c (get_seqno_by_preds): Allow returning negative
        seqno.  Adjust comment.
        * sel-sched.c (find_seqno_for_bookkeeping): Assert that when
        inserting bookkeeping before a jump, the jump is not scheduled.
        When no positive seqno found, provide a value.  Add comment.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@147977 138bc75d-0d04-0410-961f-82ee72b054a4