Enable Qt message loop on Linux

This fixes issues cause by building CEF with use_gtk=true which is the default.

Author: tytan652

cmake/os-linux.cmake

@@ -1,5 +1,7 @@
 find_package(X11 REQUIRED)
 
+target_compile_definitions(obs-browser PRIVATE ENABLE_BROWSER_QT_LOOP)
+
 target_link_libraries(obs-browser PRIVATE CEF::Wrapper CEF::Library X11::X11)
 set_target_properties(obs-browser PROPERTIES BUILD_RPATH "$ORIGIN/" INSTALL_RPATH "$ORIGIN/")