Previously were enabled only on x86_64.
Also change from using target_cpu to current_cpu, as the doc recommends.

BUG=angleproject:1814

Change-Id: Ia7e8e930c76aab5cfb47b75e0ec78902ab313237
Reviewed-on: https://chromium-review.googlesource.com/737438Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Yuly Novikov <ynovikov@chromium.org>