mosys: Run unittests with platform_test.

- This should allow the unittests to run on the actual platform.
Before, we were using a workaround where the tests ran on the
machine building mosys. This should provide better coverage.
See crbug.com/910641 for more discussion.

- This CL makes small changes to unittests and meson so they
can work with platform_test.

CQ-DEPEND=CL:1500673
BUG=chromium:910641
TEST=FEATURES='test noclean' emerge-coral mosys (a x86 device)
TEST=FEATURES='test noclean' emerge-elm mosys (an ARM device)
TEST=Pre-CQ

Change-Id: I067bfa9cffcccd1fc373d48cf2dd0cb7c4ebcbb5
Reviewed-on: https://chromium-review.googlesource.com/1500633
Commit-Ready: Andrew Lamb <andrewlamb@chromium.org>
Tested-by: Andrew Lamb <andrewlamb@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
3 files changed