SDL Build command

IF(NOT SDL_FOUND)
    ExternalProject_Add(SDL
        DOWNLOAD_DIR ""
        #URL http://www.libsdl.org/release/SDL-1.2.14.tar.gz
        URL ${CMAKE_CURRENT_SOURCE_DIR}/external/SDL.tar.gz
        SOURCE_DIR external/SDL/
        BUILD_IN_SOURCE 1
        CONFIGURE_COMMAND ./configure                                                                                                                                     
        BUILD_COMMAND make -j2
        INSTALL_COMMAND ""
        )
    SET(SDL_INCLUDE_DIR ${CMAKE_BINARY_DIR}/external/SDL/include)
    SET(SDL_LIBRARY ${CMAKE_BINARY_DIR}/external/SDL/build/libSDL.la)
    SET(SDLMAIN_LIBRARY ${CMAKE_BINARY_DIR}/external/SDL/build/libSDLmain.a)
    SET(SDL_FOUND 1)
ENDIF(NOT SDL_FOUND)