Instead of manually adopting the ancient fdlibm sources, import the msun
versions from FreeBSD instead, which were already adopted to ANSI C.
Still under the same copyright.

R=yangguo@chromium.org
BUG=v8:5065,v8:5086

Review-Url: https://codereview.chromium.org/2065473002
Cr-Commit-Position: refs/heads/master@{#36913}