Now that the hole NaN is no longer represented as Float64Constant early
on, we should never see such a constant node in any JS-level graph, but
we will only see them after representation selection. Change Typer and
SimplifiedLowering appropriately (and fix the invalid tests).

R=jarin@chromium.org
BUG=v8:5267

Review-Url: https://codereview.chromium.org/2299883003
Cr-Commit-Position: refs/heads/master@{#39063}