use SDL2 as ifdef symbol because we're not really sdl1.3 compatible, change the compatibility layer, drop unused code, add some documentation
if(WIN32 AND NOT UNIX)
file(GLOB DLLs *.dll)
file(GLOB ICOs *.ico)
install(FILES
${DLLs}
${ICOs}
DESTINATION ${target_library_install_dir})
endif(WIN32 AND NOT UNIX)