Don't define timespec in VS 2015 builds.

Don't define timespec in VS 2015 builds.

VS 2015 includes time.h from stdlib.h which leads to redefinition
warnings when threads_windows.h defines the timespec struct.

Ideally threads_windows.h shouldn't be defining CRT structs at all, but
I am doing the minimum scoped change to move VS 2015 development
forwards.

_MSC_VER == 1900 represents the VC++ 2015 compiler.

R=reillyg@chromium.org
BUG=440500
Committed: https://crrev.com/38e2756fd149695916e2948ec88f96d3ea005d23
Cr-Commit-Position: refs/heads/master@{#324133}

[brucedawson, 2015-04-07 21:09:38]

Another VS 2015 fix.

Question: why is libusb in the third_party directory when it appears to be in
the main repo?

[Reilly Grant (use Gerrit), 2015-04-07 21:14:03]

On 2015/04/07 21:09:38, brucedawson wrote:
> Another VS 2015 fix.

lgtm

> Question: why is libusb in the third_party directory when it appears to be in
> the main repo?

libusb has a number of Chromium-specific patches applied against it. It is not
the only third party library to be included directly in the main repo.

[brucedawson, 2015-04-07 21:20:52]

The CQ bit was checked by brucedawson@chromium.org

[commit-bot: I haz the power, 2015-04-07 21:21:24]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1067093002/1

[commit-bot: I haz the power, 2015-04-07 22:09:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-07 22:10:44]

Patchset 1 (id:??) landed as
https://crrev.com/38e2756fd149695916e2948ec88f96d3ea005d23
Cr-Commit-Position: refs/heads/master@{#324133}