Revert of Build the Clang plugin on Windows.

Revert of Build the Clang plugin on Windows. (patchset #7 id:120001 of https://codereview.chromium.org/1072203002/)

Reason for revert:
Rebase went horribly wrong...

Original issue's description:
> Build the Clang plugin on Windows.
>
> This also includes several fixes for the plugin logic on Windows:
> - The banned directory check normalizes path separators.
> - The banned directory check now returns true for files that are
>   considered system headers.
> - Diagnostics from the plugin are always reported as warnings.
>
> BUG=467287
> R=thakis@chromium.org
>
> Committed: https://chromium.googlesource.com/chromium/src/+/26ba172e8543b9029f320600f3aeced40028ff20
>
> Committed: https://chromium.googlesource.com/chromium/src/+/5b5d1269ade9eeb50875b20570ef3e0d8c5d95fb

TBR=hans@chromium.org,thakis@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=467287
Committed: https://crrev.com/76a1992ac341353aabea114913e9805e2f92eaa9
Cr-Commit-Position: refs/heads/master@{#325371}

[dcheng, 2015-04-16 01:38:33]

Created Revert of Build the Clang plugin on Windows.

[commit-bot: I haz the power, 2015-04-16 01:39:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1087423003/1

[commit-bot: I haz the power, 2015-04-16 01:40:05]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-16 01:41:09]

Patchset 1 (id:??) landed as
https://crrev.com/76a1992ac341353aabea114913e9805e2f92eaa9
Cr-Commit-Position: refs/heads/master@{#325371}