NACL_WIN64 takes precedence over USE_OPENSSL.

NACL_WIN64 takes precedence over USE_OPENSSL.

With the BoringSSL Windows port, it is possible for Windows to
have USE_OPENSSL set. The #ifdefs in symmetric_key.h should still
resolve in the NACL_WIN64 direction.

This fixes the crypto_nacl build target.

BUG=338884
Committed: https://crrev.com/365d6967b6b9306b90cd001ff2887189a43838e3
Cr-Commit-Position: refs/heads/master@{#301870}

[davidben, 2014-10-29 16:56:33]

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

[davidben, 2014-10-29 16:56:33]

gyp and the header disagree on which takes precedence.

[Ryan Sleevi, 2014-10-29 17:06:12]

The CQ bit was checked by rsleevi@chromium.org

[Ryan Sleevi, 2014-10-29 17:06:13]

lgtm

[commit-bot: I haz the power, 2014-10-29 17:07:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/689463002/1

[commit-bot: I haz the power, 2014-10-29 17:51:35]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-29 17:52:39]

Patchset 1 (id:??) landed as
https://crrev.com/365d6967b6b9306b90cd001ff2887189a43838e3
Cr-Commit-Position: refs/heads/master@{#301870}