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This reverts commit 174d9faa.

Reason for revert: Breaking https://ci.chromium.org/p/chromium/builders/ci/chromeos-amd64-generic-cfi-thin-lto-rel

See:
https://ci.chromium.org/p/chromium/builders/ci/chromeos-amd64-generic-cfi-thin-lto-rel/24710

Original change's description:
> build: In LTO links, run just one link at once, but give it all cores
>
> Normally, we allow running several links in parallel if there's enough
> memory, since links tend to be memory- and io-bound, not compute bound.
> However, in LTO builds the linker does codegen for every linked
> translation unit, which needs a lot of CPU.
>
> Previously, we used to hardcode 8 threads per link for thinlto builds,
> which makes builds needlessly slow on machines with many cores.
>
> Instead, automatically use all cores for a thinlto link, but only run
> one link in parallel at once.
>
> chromeos-chrome-9999.ebuild in the Chrome OS build and link_jobs_32 in
> mb_config.pyl currently manually set the number of threads per lto link
> to the number of cores. Once this change here is in, we should stop
> explicitly setting the arg there and then we can turn this from a gn arg
> to a regular variable that's not settable in args.gn
>
> Bug: 1132930
> Change-Id: If2fda3e38b2b1827beb2da844f024f52211210db
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2464782
> Reviewed-by: Hans Wennborg <hans@chromium.org>
> Commit-Queue: Nico Weber <thakis@chromium.org>
> Auto-Submit: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#816129}

TBR=thakis@chromium.org,hans@chromium.org

Change-Id: Ic1d381681e00dbebd576ec44119d426518f4b778
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1132930
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2466261Reviewed-by: Moe Ahmadi <mahmadi@chromium.org>
Commit-Queue: Moe Ahmadi <mahmadi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#816208}