port f2da19fe (r36703)

  original commit message:
  Introduce a dedicated Float64Log machine operator, that is either
  implemented by a direct C call or by platform specific code, i.e.
  using the FPU on x64 and ia32.

  This operator is used to implement Math.log as a proper TurboFan
  builtin on top of the CodeStubAssembler.

  Also introduce a NumberLog simplified operator on top of Float64Log
  and use that for the fast inline path of Math.log inside TurboFan
  optimized code.

BUG=

Review-Url: https://codereview.chromium.org/2034393002
Cr-Commit-Position: refs/heads/master@{#36727}