Enable ThinLTO for POSIX LTO by default on Linux, take 2.
Previous attempt: https://codereview.chromium.org/2939373002
It was reverted because it caused large thinlto-cache directories
to be created on the perf bots, which were also being unnecessarily
included in package archives. This has been addressed in two ways:
1) the bots have been taught to exclude thinlto-cache from
package archives (see https://chromium-review.googlesource.com/c/544530/).
2) this change limits the size of the cache to 10% of
available disk space.
BUG=660216,735651
R=dpranke@chromium.org,thakis@chromium.org
TBR=thomasanderson@chromium.org
Review-Url: https://codereview.chromium.org/2957533002
Cr-Commit-Position: refs/heads/master@{#481944}
3 files changed
