Fix OSX compilation of trianglell example due to lack of d3d12 or vulkan support.
Fix OSX compilation of trianglell example due to lack of d3d12 or vulkan support.

tanderegg/gfx,gfx-rs/gfx-rs,tanderegg/gfx,davll/gfx,JohnColanduoni/gfx,JohnColanduoni/gfx,ColinKinloch/gfx,ColinKinloch/gfx