Copy the Vulkan-related dependencies into the 'unix' section of the file
so we linux bots can build ANGLE's Vulkan backend.

BUG=angleproject:1668

Change-Id: I79e2895b525808072495c7cf18138facef6cc868
Reviewed-on: https://chromium-review.googlesource.com/475085
Commit-Queue: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>