FindVulkan: Disable system paths - this fixes discovery on 32-bit Windows & SDK versions < 1.0.42.
Before Vulkan 1.0.42, the SDK would add the
Bin directory to
PATH, which was confusing the 32-bit search on Windows. Vulkan 1.0.42 fixed the whole problem by moving the libraries into
Lib32, so this is strictly a compatibility fix for old SDKs.