OpenGL hello.c fails to build using CMake
===

I am trying to build the hello.c example from http://www.glprogramming.com/red/chapter01.html (look for "Example 1-2").

My CMakeLists.txt is as follows:

    cmake_minimum_required (VERSION 2.8)
    project (GLUTEX)
    
    find_package(OpenGL REQUIRED)
    find_package(GLUT REQUIRED)
    include_directories(${GLUT_INCLUDE_DIRS})
    include_directories(${OpenGL_INCLUDE_DIRS})
    
    add_executable (glutex glutex.c)
    target_link_libraries (glutex ${OpenGL_LIBRARIES})
    target_link_libraries (glutex ${GLUT_LIBRARIES})

The CMake call succeeds in generating the required Makefile. But when I call `make`, I encounter the following:

    Scanning dependencies of target glutex
    [100%] Building C object CMakeFiles/glutex.dir/glutex.c.o
    Linking C executable glutex
    /usr/bin/ld: CMakeFiles/glutex.dir/glutex.c.o: undefined reference to symbol 'glOrtho'
    /usr/bin/ld: note: 'glOrtho' is defined in DSO /usr/lib64/libGL.so.1 so try adding it to the linker command line
    /usr/lib64/libGL.so.1: could not read symbols: Invalid operation
    collect2: ld returned 1 exit status
    make[2]: *** [glutex] Error 1
    make[1]: *** [CMakeFiles/glutex.dir/all] Error 2
    make: *** [all] Error 2

How do I fix this?
