Disable Vulkan support on Linux
Disable Vulkan support on Linux

There are both compile error and missing build file dependencies in
standalone builds.

BUG=angleproject:1668

Change-Id: I8741bd3dd20452c94921101bbf7c5be39fb463b7
Reviewed-on: https://chromium-review.googlesource.com/493608
Reviewed-by: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>
Commit-Queue: Corentin Wallez <470c533e86f4f848c98c7e11fffc2d043494a401@chromium.org>

MSOpenTech/angle,ppy/angle,ecoal95/angle,MSOpenTech/angle,MSOpenTech/angle,ppy/angle,ppy/angle,ecoal95/angle,ecoal95/angle,ecoal95/angle,ppy/angle,MSOpenTech/angle,ecoal95/angle