Disable size_t truncation warning (C4267) on BoringSSL Win64.

Disable size_t truncation warning (C4267) on BoringSSL Win64.

There's a ton of them; OpenSSL is very far from being size_t-clean. Disable
the warning (as in the standalone build's cmake setup) until we get a handle
on it in BoringSSL.

BUG=429039, 167187
Committed: https://crrev.com/d6461f32e4e9c7274083604cd30290c1739b91fb
Cr-Commit-Position: refs/heads/master@{#302857}

[davidben, 2014-10-31 19:00:41]

davidben@chromium.org changed reviewers:
+ agl@chromium.org

[davidben, 2014-10-31 19:00:42]

Turns out this is still not sufficient to get things building on Win64, but it's
a start.

(Still trying to sort out the other issue. out/Debug + target_arch=x64 knows
about assembly but is configured for an x86 toolchain, while out/Debug_x64 +
target_arch=x64 is configured for an x64 toolchain but doesn't know about the
assembly. I vaguely suspect we may want to yasm the x64 side as well.)

[agl, 2014-11-05 18:53:50]

LGTM.

(P.s. if I've not replied to a CL in days but am otherwise responsive then I
missed the email. Please ping.)

[davidben, 2014-11-05 19:22:54]

The CQ bit was checked by davidben@chromium.org

[commit-bot: I haz the power, 2014-11-05 19:24:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/684093011/20001

[commit-bot: I haz the power, 2014-11-05 20:11:50]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-11-05 20:13:43]

Patchset 2 (id:??) landed as
https://crrev.com/d6461f32e4e9c7274083604cd30290c1739b91fb
Cr-Commit-Position: refs/heads/master@{#302857}