GitLab

This is a reland of 1501aabf
The goma failures which caused the previous revert are believe to be flaky.

Original change's description:
> Clang: stop building with GCC/libstdc++ from Ubuntu Precise (roll 338452-1:338452-2)
>
> Previously we used a GCC/libstdc++ package from Ubuntu Precise to build a Clang
> that would work on Precise or later. These days, all bots and developers are on
> Trusty or later, so this should no longer be necessary.
>
> Bug: none
> Change-Id: I518ee55d07c04dc89163fe262c81d935e05fed78
> Reviewed-on: https://chromium-review.googlesource.com/1183915
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
> Commit-Queue: Hans Wennborg <hans@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#585067}

TBR=thakis

Bug: none
Change-Id: Ibd2be5064bbdf0ed36aa09c0525825c530465813
Reviewed-on: https://chromium-review.googlesource.com/1185684Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585318}