Fix build/secondary/third_party/nss/BUILD.gn on iOS.

Fix build/secondary/third_party/nss/BUILD.gn on iOS.

Compilers configuration have been moved from //build/compiler to
//build/config/compiler, update //third_party/nss when targetting
iOS.

BUG=459705
Committed: https://crrev.com/768d90d3853fa121580923b0944998354c592a01
Cr-Commit-Position: refs/heads/master@{#340057}

[sdefresne, 2015-07-22 16:45:07]

sdefresne@chromium.org changed reviewers:
+ dpranke@chromium.org

[sdefresne, 2015-07-22 16:45:07]

PTAL

[Dirk Pranke, 2015-07-22 16:45:52]

lgtm

[sdefresne, 2015-07-23 07:50:04]

The CQ bit was checked by sdefresne@chromium.org

[commit-bot: I haz the power, 2015-07-23 07:50:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1249053002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1249053002/1

[commit-bot: I haz the power, 2015-07-23 08:29:20]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-07-23 08:29:54]

Patchset 1 (id:??) landed as
https://crrev.com/768d90d3853fa121580923b0944998354c592a01
Cr-Commit-Position: refs/heads/master@{#340057}