It seems we produce both the usual add as well as the add with
overflow, when we should only generate the overflow variant. This
invalidates SSA assumptions in 2 tests (cctest/test-run-machops/RunInt32AddWithOverflowImm and
cctest/test-run-machops/RunInt64AddWithOverflowImm).

BUG=

Review URL: https://codereview.chromium.org/1757213003

Cr-Commit-Position: refs/heads/master@{#34507}