iOS: Use a 10.7 deployment target for host builds.
iOS: Use a 10.7 deployment target for host builds.

The internal iOS build used to use libstdc++, but after
https://codereview.chromium.org/1334273004/ force libc+++ on for iOS the
internal bots broke because they use Xcode's clang and Xcode's clang
complains if -stdlib=libc++ is passed and the deployment target is not at
least 10.7.

As a fix, set the mac deployment target for iOS host compiles to 10.7, and
suppress warnings about deprecated functions for iOS host compiles.  (The
warnings can't be fixed until the deployment target is increased on Mac too;
this is covered by crbug.com/547071)

BUG=535104,400091

Review URL: https://codereview.chromium.org/1426433002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#355822}

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