title: The C compiler identification is unknown
body: <p>I want to compile a C program.  When I run <code>cmake</code></p>
  
  <pre><code>   build]$ cmake ../
      -- The C compiler identification is unknown
      -- Check for working C compiler: /usr/bin/cc
      -- Check for working C compiler: /usr/bin/cc -- broken
      CMake Error at /usr/share/cmake-3.0/Modules/CMakeTestCCompiler.cmake:61 (message):
        The C compiler "/usr/bin/cc" is not able to compile a simple test program.
  </code></pre>
  
  <p>It fails with the following output:</p>
  
  <pre><code>   Change Dir: /home/vahid/dev/Indexer/build/CMakeFiles/CMakeTmp
  
    Run Build Command:"/usr/bin/make" "cmTryCompileExec3431547622/fast"
  
    /usr/bin/make -f CMakeFiles/cmTryCompileExec3431547622.dir/build.make
    CMakeFiles/cmTryCompileExec3431547622.dir/build
  
    make[1]: Entering directory
    '/home/vahid/dev/Indexer/build/CMakeFiles/CMakeTmp'
  
    /usr/bin/cmake -E cmake_progress_report
    /home/vahid/dev/Indexer/build/CMakeFiles/CMakeTmp/CMakeFiles 1
  
    Building C object
    CMakeFiles/cmTryCompileExec3431547622.dir/testCCompiler.c.o
  
    /usr/bin/cc -o CMakeFiles/cmTryCompileExec3431547622.dir/testCCompiler.c.o
    -c /home/vahid/dev/Indexer/build/CMakeFiles/CMakeTmp/testCCompiler.c
  
    /usr/lib/gcc/x86_64-unknown-linux-gnu/4.9.0/cc1: error while loading shared
    libraries: libisl.so.13: cannot open shared object file: No such file or
    directory
  
    CMakeFiles/cmTryCompileExec3431547622.dir/build.make:57: recipe for target
    'CMakeFiles/cmTryCompileExec3431547622.dir/testCCompiler.c.o' failed
  
    make[1]: *** [CMakeFiles/cmTryCompileExec3431547622.dir/testCCompiler.c.o]
    Error 1
  
    make[1]: Leaving directory
    '/home/vahid/dev/Indexer/build/CMakeFiles/CMakeTmp'
  
    Makefile:118: recipe for target 'cmTryCompileExec3431547622/fast' failed
  
    make: *** [cmTryCompileExec3431547622/fast] Error 2
  
  
    CMake will not be able to correctly generate this project.
  Call Stack (most recent call first):
    CMakeLists.txt:2 (project)
  
  
  -- Configuring incomplete, errors occurred!
  See also "/home/vahid/dev/Indexer/build/CMakeFiles/CMakeOutput.log".
  See also "/home/vahid/dev/Indexer/build/CMakeFiles/CMakeError.log".
  </code></pre>
  
  <p>why did this error occur?  How can I fix it?</p>