Rewrite some tests with FileCHeck in X86 codegen

- Revise previous patches of the same purpose by fixing
  *) grep <PA> | not grep <PB> semantically is not the same as
     CHECK: <PA>{{^<PB>.*$}} as the former will check all occurrences of <PA>
     while the later only check the first match. As the result, CHECK needs
     putting in all place where <PA> occurs.
  *) grep <PA> | count <N> needs a final CHECK-NOT of the same pattern.
     (As 'CHECK-<N>' is proposed for discussion, converting 'grep | count <N>'
      where N > 1 is postponed.)