cmake HAVE_SHMAT_IN_IPC examples

AtomicGameEngine/AtomicGameEngine Source/ThirdParty/SDL/cmake/sdlchecks.cmake :429 

check_library_exists(ipc shmat "" HAVE_SHMAT_IN_IPC)

urho3d/urho3d Source/ThirdParty/SDL/cmake/sdlchecks.cmake :443 

check_library_exists(ipc shmat "" HAVE_SHMAT_IN_IPC)