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Cherry pick rtcd-related changes and re-run cmake_update.sh

This allows the linker to remove unused C code when an sse2 version
is available. See discussion on libvpx:
https://chromium-review.googlesource.com/c/chromium/src/+/1195800

R=tomfinegan@chromium.org

Change-Id: I419a87e6d0b4f9166754aaaedf6b9c8cd1834dae
Reviewed-on: https://chromium-review.googlesource.com/1197466Reviewed-by: Tom Finegan <tomfinegan@chromium.org>
Commit-Queue: Johann Koenig <johannkoenig@google.com>
Cr-Commit-Position: refs/heads/master@{#587780}