USE_SLANG currently disregards whether USE_WAYLAND was used or not
and leads to trying to use wayland headers that may be missing.

--- snes9x-1.63/gtk/CMakeLists.txt
+++ snes9x-1.63/gtk/CMakeLists.txt
@@ -105,13 +105,15 @@
     list(APPEND INCLUDES "../external/glslang")
 
     list(APPEND DEFINES "VK_USE_PLATFORM_XLIB_KHR"
-                        "VK_USE_PLATFORM_WAYLAND_KHR"
                         "VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=1"
                         "VULKAN_HPP_NO_NODISCARD_WARNINGS=1"
                         "VULKAN_HPP_NO_EXCEPTIONS=1"
                         "VMA_DYNAMIC_VULKAN_FUNCTIONS=1"
                         "VMA_STATIC_VULKAN_FUNCTIONS=0"
                         "IMGUI_IMPL_VULKAN_NO_PROTOTYPES")
+    if(USE_WAYLAND)
+	list(APPEND DEFINES "VK_USE_PLATFORM_WAYLAND_KHR")
+    endif()
     list(APPEND INCLUDES ../external/vulkan-headers/include)
     list(APPEND INCLUDES ../external/VulkanMemoryAllocator-Hpp/include)
     list(APPEND INCLUDES ../external/stb)