Clusterfuzz generated test cases for narrow Load, CmpExchg nodes in
which the index is a word64 expression. This was not handled correctly
leading to a malformed graph. Use default lowering for all atomic
narrow operations, and add reduced test cases in wasm cctests with the
same sequence as the ones generated by binaryen for other I64Atomic
operations as well.

Change-Id: I50d63747b16a8f69289ca4e76547b325d84b22d3
Bug: chromium:921366, chromium:920120, chromium:900681
Reviewed-on: https://chromium-review.googlesource.com/c/1423177
Commit-Queue: Deepti Gandluri <gdeepti@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59012}