Instead of using a sequence

  if (something == null && !IS_UNDETECTABLE(something))) { ... }

which will be true if something is either null or undefined, it is
way simpler and way more efficient to just write

  if (something === null || something === (void 0)) { ... }

instead, which allows the compiler(s) to generate pretty decent code
without any need to resort to type feedback from a CompareNil IC.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/1288623003

Cr-Commit-Position: refs/heads/master@{#30135}