This CL fixes two unrelated issues in Turbofan that contributed to
non-determinism:
- Most importantly, external references included their address in the
  node hash, but they're unpredictable due to ASLR. Fix by only looking
  at the lowest bits assuming a 4K page size.
- BranchElimination didn't properly trigger revisits for the
  IfTrue/IfFalse projections.

Bug: chromium:1046815
Change-Id: I9ba3535cc748890708e4638017e245a3f4e2a7d8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2069332
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66445}