GitLab

This relands commit 1ba5d611.

Fixes chromeos build issue by checking whether we have a secondary
toolchain before comparing it with the current toolchain.

Original change's description:
> build: Enable ThinLTO in official Android builds.
>
> With this change we start building Chromium with ThinLTO when targeting
> Android. In 64-bit Monochrome builds, the 32-bit binary is also built
> with ThinLTO. This change is expected to reduce code size significantly
> (in local measurements it reduced the size of MonochromePublic.apk by 2.3MB)
> and is a prerequisite for enabling control flow integrity in official
> builds.
>
> Note that although this change enables ThinLTO, it does not enable
> the cross-TU optimizations normally associated with LTO. Enabling
> cross-TU optimizations is a separate project.
>
> On my local machine (a Lenovo P920) libmonochrome.so link times increase
> as follows:
>
>          before  after (first link)  after (incremental links)
> 32-bit    18s          140s                     50s
> 64-bit    13s          107s                     41s
>
> All known blockers have now been fixed. This CL is likely to uncover
> unknown blockers.
>
> Bug: 469376
> Change-Id: I8981e17abd50bc5ca00440e0d74dda878c911749
> Reviewed-on: https://chromium-review.googlesource.com/1150870
> Commit-Queue: Peter Collingbourne <pcc@chromium.org>
> Reviewed-by: Nico Weber <thakis@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#578195}

Bug: 469376, 868426
Change-Id: Ie46ba0db0ac68130bc600415777de5c813b28ebd
Reviewed-on: https://chromium-review.googlesource.com/1153612Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Peter Collingbourne <pcc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578854}