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This gets us off the hook from fixing failures in a build config which
is not well tested upstream, reduces the package build time, and
simplifies our build script.

It also make thinlto faster, due to lld now being built with PGO
(although we don't train on lld, it benefits from the training on clang).

Bug: 884608, 949626
Change-Id: I55859efbde9071da72c1057765d0d1900e069eea
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2095544Reviewed-by: Reid Kleckner <rnk@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#749607}