Import base::ieee754::log1p() from fdlibm and introduce a Float64Log1p
TurboFan operator based on that, similar to what we do for Float64Log.
Rewrite Math.log1p() as TurboFan builtin and use that operator to also
inline Math.log1p() into optimized TurboFan functions.

Also unify the handling of the special IEEE 754 functions somewhat in
the TurboFan backends. At some point we can hopefully express this
completely in the InstructionSelector (once we have an idea what to do
with the ST(0) return issue on IA-32/X87).

Drive-by-fix: Add some more test coverage for the log function.

R=yangguo@chromium.org
BUG=v8:5086,v8:5092

Review-Url: https://codereview.chromium.org/2060743002
Cr-Commit-Position: refs/heads/master@{#36914}