build: disable VK if WARP_ONLY set

[Keenuts]

Current build logic enables Vulkan if the headers are found, even when WARP_ONLY is set to On. This can happen when the Vulkan SDK is in the path. This causes issues on machine with no Vulkan implementation available as building with Vulkan support enabled will require the vulkan DLL to be present.

[s-perron]

I'm with @farzonl. Can you explain the actual problem? Is there a more general problem that we might have the vulkan include dirs, but no vulkan driver, then the problem has nothing to do with warp. We should fix that problem, which could happen in other situations.

If the problem is that the option "OFFLOADTEST_WARP_ONLY" suggests that we should not build with Vulkan, even if everything works, then I would say leave it on if there is a vulkan driver. The documentation says it "Skips generating d3d test configurations for non-WARP configurations." It does not say it skips Vulkan.

If you want it to skip Vulkan with that option, you should update the documentation for it.

[Keenuts]

I'm with @farzonl. Can you explain the actual problem? Is there a more general problem that we might have the vulkan include dirs, but no vulkan driver, then the problem has nothing to do with warp. We should fix that problem, which could happen in other situations.

If the problem is that the option "OFFLOADTEST_WARP_ONLY" suggests that we should not build with Vulkan, even if everything works, then I would say leave it on if there is a vulkan driver. The documentation says it "Skips generating d3d test configurations for non-WARP configurations." It does not say it skips Vulkan.

If you want it to skip Vulkan with that option, you should update the documentation for it.

#742 (comment)
I explained the problem in the comment thread.

[Keenuts]

@s-perron anything else?

[s-perron]

The "warp only" wording makes it make sense that Vulkan would be excluded, so I'm okay with it with the docs update.