libobs: Add a Wayland platform

Introduce the OBS_NIX_PLATFORM_WAYLAND enum value, and try to detect
it when OBS Studio runs by looking into the platform name.

UI/CMakeLists.txt

@@ -396,6 +396,16 @@ if(WIN32)
 			OUTPUT_NAME "obs${_output_suffix}")
 endif()
 
+if (ENABLE_WAYLAND)
+	find_package(Qt5Gui REQUIRED)
+	include_directories(${Qt5Gui_PRIVATE_INCLUDE_DIRS})
+
+	set(obs_PLATFORM_LIBRARIES
+		${obs_PLATFORM_LIBRARIES}
+		Qt5::Gui
+		Qt5::GuiPrivate)
+endif()
+
 target_link_libraries(obs
 	libobs
 	Qt5::Widgets