According to the WebAssembly spec no arithmetic operation should ever
return a signalling NaN. With the constant folding in V8, however, it
was possible that some arithmetic operations were elided, and if the
input of the arithmetic operation was a signalling NaN, then also the
result was the same signalling NaN. This CL removes some constant
folding optimizations and adjusts others so that even with constant
folding the result of an arithmetic operation is never a signalling NaN.

R=titzer@chromium.org, rossberg@chromium.org, bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/2647353007
Cr-Commit-Position: refs/heads/master@{#42694}