CMake SDL : undefined reference to

I'm working on a project using the SDL (v1.2.15-7) and cmake (3.2.1). In the *.h files I added the #include <SDL.h> and when I compile it, I have a bunch of errors : undefined reference to SDL_...

I think the mistake comes from the CMakeLists.txt but I really don't know where.

Here's the file content :

    CMAKE_MINIMUM_REQUIRED( VERSION 2.8 )

    SET( PROJ_NAME      "Project" )
    SET( PROJ_PATH      ${CMAKE_SOURCE_DIR} )
    SET( PROJ_OUT_PATH  ${CMAKE_BINARY_DIR} )
    SET( PROJ_INCLUDES  "include" )

    FILE( GLOB_RECURSE PROJ_SOURCES src/*cpp test/*cpp doc/*)
    FILE( GLOB_RECURSE PROJ_HEADERS ${PROJ_INCLUDES}/${PROJ_NAME}/*.h )

    PROJECT( ${PROJ_NAME} )

    SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++0x")

    FIND_PACKAGE( SDL REQUIRED )

    SET( PROJ_LIBRARIES ${SDL_LIBS} )

    INCLUDE_DIRECTORIES( ${PROJ_INCLUDES} ${SDL_INCLUDE_DIR} )
    ADD_EXECUTABLE( ${PROJ_NAME} ${PROJ_SOURCES} ${PROJ_HEADERS} )
    TARGET_LINK_LIBRARIES( ${PROJ_NAME} ${PROJ_LIBRARIES} )

If you need more information ask.

PS : I also tried #include SDL/SDL.h

Thanks in advance.