Fix fallout from https://codereview.chromium.org/678423002/

Fix fallout from https://codereview.chromium.org/678423002/

* Let BUILD.gn build the same files on Windows as the gyp file does.
* Remove -msse2 flag, that's on globally
* On win/clang, pass -msse4.2 -mclmul flags to fix clang/wi
  complaining about unsupported intrinsics

BUG=82385
R=dpranke@chromium.org, hans@chromium.org
TBR=brettw

Committed: https://crrev.com/f3b5bb2d25abb3bacb246531b6cfa6d36abb17b2
Cr-Commit-Position: refs/heads/master@{#304695}

[Nico, 2014-11-18 22:58:21]

thakis@chromium.org changed reviewers:
+ dpranke@chromium.org, hans@chromium.org

[Nico, 2014-11-18 22:58:22]

dpranke: gn change
hans: gyp change

[Dirk Pranke, 2014-11-18 23:03:01]

lgtm

[hans, 2014-11-18 23:06:11]

lgtm

[Nico, 2014-11-18 23:06:35]

The CQ bit was checked by thakis@chromium.org

[commit-bot: I haz the power, 2014-11-18 23:09:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/742583003/1

[commit-bot: I haz the power, 2014-11-18 23:22:48]

Patchset 1 (id:??) landed as
https://crrev.com/f3b5bb2d25abb3bacb246531b6cfa6d36abb17b2
Cr-Commit-Position: refs/heads/master@{#304695}

[Nico, 2014-11-18 23:22:50]

Committed patchset #1 (id:1) manually as
f3b5bb2d25abb3bacb246531b6cfa6d36abb17b2 (presubmit successful).