In practice, Emscripten seems to emit cond?+a:+b type return
expressions. This is not allowed by the spec or errata, but we need
to support it for compatibility.

Similar patterns with ints / signed, do not seem to be supported.

BUG=v8:5891
R=mtrofin@chromium.org,aseemgarg@chromium.org

Review-Url: https://codereview.chromium.org/2648353010
Cr-Commit-Position: refs/heads/master@{#42677}