Revert of Build: Don't pass /GL to Clang on Windows

Revert of Build: Don't pass /GL to Clang on Windows (patchset #3 id:40001 of https://codereview.chromium.org/1186743002/)

Reason for revert:
Broke some official builds (http://crbug.com/500393). Will roll clang forward instead.

Original issue's description:
> Build: Don't pass /GL to Clang on Windows
>
> Windows Clang's support for LTO isn't ready to take on Chrome yet.
>
> BUG=82385
> R=thakis@chromium.org
> TBR=scottmg
>
> Committed: https://chromium.googlesource.com/chromium/src/+/4e76e7926ee51bdfdd635437920f455ae6444912

TBR=scottmg@chromium.org,hans@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=82385
Committed: https://crrev.com/7ec6a579b7e47f84b384b98b6f04ee65beb55758
Cr-Commit-Position: refs/heads/master@{#334419}

[Nico, 2015-06-15 18:24:31]

Created Revert of Build: Don't pass /GL to Clang on Windows

[commit-bot: I haz the power, 2015-06-15 18:24:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1185133004/1

[commit-bot: I haz the power, 2015-06-15 18:27:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-06-15 18:27:59]

Patchset 1 (id:??) landed as
https://crrev.com/7ec6a579b7e47f84b384b98b6f04ee65beb55758
Cr-Commit-Position: refs/heads/master@{#334419}