Port f2da19fe

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.

R=bmeurer@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=v8:5065
LOG=N

Review-Url: https://codereview.chromium.org/2036273002
Cr-Commit-Position: refs/heads/master@{#36720}