[dxvk] Disable VrInstance and DxvkXrProvider on native builds

If/when we want to support VR on native builds, we can deal with that then.

src/dxvk/dxvk_instance.cpp

@@ -20,8 +20,10 @@ namespace dxvk {
     m_options = DxvkOptions(m_config);
 
     m_extProviders.push_back(&DxvkPlatformExts::s_instance);
+#ifdef _WIN32
     m_extProviders.push_back(&VrInstance::s_instance);
     m_extProviders.push_back(&DxvkXrProvider::s_instance);
+#endif
 
     Logger::info("Built-in extension providers:");
     for (const auto& provider : m_extProviders)