GN: Add system_wrappers_unittests, tools and tools_unittests

BUG=webrtc:5949
TESTED=Built and ran the tests on Mac.
NOTRY=True

Review-Url: https://codereview.webrtc.org/2025343002
Cr-Original-Commit-Position: refs/heads/master@{#13007}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: bac0412e7f32ab8c7bfc14ddf263ccec20d92a37
5 files changed