This fixes a bot compilation failure that started happening after
unittest started using Display stuff that use X11. Because
angle_unittests was linking against libANGLE and not libGLESv2, it
didn't get linked to X11, which produced a link error.

BUG=

Change-Id: I8f1f0dbcb13bb7c9897f235b72c4d4896a7b8a6c
Reviewed-on: https://chromium-review.googlesource.com/292380Tested-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>