Add back support for /Gv now that gyp-win64 has VS2013

Add back support for /Gv now that gyp-win64 has VS2013

This was removed in the last minute in r1984 because of failures in the
gyp-win64 bot.

BUG=
R=scottmg@chromium.org

Committed: https://code.google.com/p/gyp/source/detail?r=2007

[Shezan Baig (Bloomberg), 2014-10-10 22:24:52]

sbaig1@bloomberg.net changed reviewers:
+ scottmg@chromium.org

[scottmg, 2014-10-10 22:29:37]

It's still running on 2012, I'll send you a CL to switch it.

[Shezan Baig (Bloomberg), 2014-10-12 12:04:32]

On 2014/10/10 22:29:37, scottmg wrote:
> It's still running on 2012, I'll send you a CL to switch it.

I've updated the vectorcall test to only run if we are using at least 2013. 
I'll wait for your CL to land before I send this to try bots.  Thanks!

[scottmg, 2014-11-19 20:13:30]

Sorry, forgot about this, should be landable now. lgtm.

[Shezan Baig (Bloomberg), 2014-11-19 20:21:54]

On 2014/11/19 20:13:30, scottmg wrote:
> Sorry, forgot about this, should be landable now. lgtm.

Thanks!  Is it OK to bypass presubmit checks to land this?  The new pylint is
generating a lot of errors :(

[scottmg, 2014-11-19 20:24:26]

On 2014/11/19 20:21:54, Shezan Baig (Bloomberg) wrote:
> On 2014/11/19 20:13:30, scottmg wrote:
> > Sorry, forgot about this, should be landable now. lgtm.
> 
> Thanks!  Is it OK to bypass presubmit checks to land this?  The new pylint is
> generating a lot of errors :(

If they're not new, it seems fine to me. We should see if any are important I
guess, but that seems unrelated to this.

[Shezan Baig (Bloomberg), 2014-11-19 20:27:42]

On 2014/11/19 20:24:26, scottmg wrote:
> On 2014/11/19 20:21:54, Shezan Baig (Bloomberg) wrote:
> > On 2014/11/19 20:13:30, scottmg wrote:
> > > Sorry, forgot about this, should be landable now. lgtm.
> > 
> > Thanks!  Is it OK to bypass presubmit checks to land this?  The new pylint
is
> > generating a lot of errors :(
> 
> If they're not new, it seems fine to me. We should see if any are important I
> guess, but that seems unrelated to this.


Created https://code.google.com/p/gyp/issues/detail?id=469
I'm gonna take a look at the pylint errors later today/tomorrow.  Hopefully I
can clean them up and then I'll land this cleanly.

[Shezan Baig (Bloomberg), 2014-11-21 14:30:04]

Committed patchset #4 (id:220001) manually as 2007 (presubmit successful).