CMake: Allow disabling Wayland support with USE_WAYLAND_WSI

This change means that USE_WAYLAND_WSI=ON no longer triggers a
fatal error if Wayland libraries are missing though, it will just
show a message and continue building without Wayand WSI support.

Closes #11536.

CMakeLists.txt

@@ -122,6 +122,7 @@ option(USING_FBDEV "Set to ON if target environment uses fbdev (eg. Pandora)" ${
 option(USING_GLES2 "Set to ON if target device uses OpenGL ES 2.0" ${USING_GLES2})
 option(RASPBIAN "Set to ON to workaround threading issues when building for ARMV7 on Raspbian" ${RASPBIAN})
 option(USING_X11_VULKAN "Set to OFF if target environment doesn't use X11 for Vulkan" ON)
+option(USE_WAYLAND_WSI "Enable or disable Wayland WSI support for Vulkan" ON)
 # :: Frontends
 option(USING_QT_UI "Set to ON if you wish to use the Qt frontend wrapper" ${USING_QT_UI})
 option(MOBILE_DEVICE "Set to ON when targeting a mobile device" ${MOBILE_DEVICE})
@@ -134,7 +135,6 @@ option(USE_FFMPEG "Build with FFMPEG support" ${USE_FFMPEG})
 option(USE_SYSTEM_SNAPPY "Dynamically link against system snappy" ${USE_SYSTEM_SNAPPY})
 option(USE_SYSTEM_FFMPEG "Dynamically link against system FFMPEG" ${USE_SYSTEM_FFMPEG})
 option(USE_SYSTEM_LIBZIP "Dynamically link against system libzip" ${USE_SYSTEM_LIBZIP})
-option(USE_WAYLAND_WSI "Set to ON to require Wayland support for Vulkan" ${USE_WAYLAND_WSI})
 option(USE_ADDRESS_SANITIZER "Use Clang memory sanitizer" ${USE_ADDRESS_SANITIZER})
 
 if(UNIX AND NOT (APPLE OR ANDROID) AND VULKAN)
@@ -145,13 +145,14 @@ if(UNIX AND NOT (APPLE OR ANDROID) AND VULKAN)
 		message("NOT using X11 for Vulkan")
 	endif()
 	# add_definitions(-DVK_USE_PLATFORM_XCB_KHR)
-	find_package(Wayland)
-	if(USE_WAYLAND_WSI AND NOT WAYLAND_FOUND)
-		message(FATAL_ERROR "Could not find libwayland, but USE_WAYLAND_WSI was enabled. Failing.")
-	endif()
-	if(WAYLAND_FOUND)
-		include_directories(${WAYLAND_INCLUDE_DIR})
-		add_definitions(-DVK_USE_PLATFORM_WAYLAND_KHR)
+	if(USE_WAYLAND_WSI)
+		find_package(Wayland)
+		if(NOT WAYLAND_FOUND)
+			message(STATUS "Could not find Wayland libraries, disabling Wayland WSI support for Vulkan.")
+		else()
+			include_directories(${WAYLAND_INCLUDE_DIR})
+			add_definitions(-DVK_USE_PLATFORM_WAYLAND_KHR)
+		endif()
 	endif()
 endif()