Flaky MergeICmps/X86 test on llvm-clang-x86_64-expensive-checks-win

It looks like there's a flaky test, maybe someone who understands
the relevant area can take a closer look. I noticed because the
same failure showed up twice as blame mail from my recent series
of commits. This test:


will sometimes fail on llvm-clang-x86_64-expensive-checks-win.
I don't claim any expertise but the intervening commits don't
really look like they would cause or fix these failures.

Build #
17607 pass (although another test failed)
17608 pass
17609 FAIL
17610 FAIL
17611 pass
17612 pass
17613 FAIL
17614 pass
17615 pass
17616 FAIL
17617 FAIL
17618 pass
17619 pass

See for example