The wasm specification does not fully specify the binary representation
of NaN: the sign bit can be non-deterministic. The wasm-code fuzzer
found a test case where the wasm interpreter and the compiled code
produce a different sign bit for a NaN, and as a consequence they
produce different results.

With this CL the interpreter tracks whether it executed an instruction
which can produce a NaN, which are div and sqrt instructions. The
fuzzer uses this information and compares the result of the interpreter
with the result of the compiled code only if there was no instruction
which could have produced a NaN.

R=titzer@chromium.org

TEST=cctest/test-run-wasm-interpreter/TestMayProduceNaN
BUG=chromium:657481

Review-Url: https://chromiumcodereview.appspot.com/2438603003
Cr-Commit-Position: refs/heads/master@{#40474}