title: Can't run Cmake on windows with MinGW and git bash
body: <p>I try to build <a href="https://github.com/cloudson/gitql" rel="noreferrer">gitql</a>.</p>
  
  <p>I've installed go, CMake and MinGW, and tried to make them work under git bash, but when I call cmake in gitql directory I get this error:</p>
  
  <pre><code>-- Building for: NMake Makefiles
  -- The C compiler identification is unknown
  CMake Error at CMakeLists.txt:14 (PROJECT):
    The CMAKE_C_COMPILER:
  
      cl
  
    is not a full path and was not found in the PATH.
  
    To use the NMake generator with Visual C++, cmake must be run from a shell
    that can use the compiler cl from the command line.  This environment is
    unable to invoke the cl compiler.  To fix this problem, run cmake from the
    Visual Studio Command Prompt (vcvarsall.bat).
  
    Tell CMake where to find the compiler by setting either the environment
    variable "CC" or the CMake cache entry CMAKE_C_COMPILER to the full path to
    the compiler, or to the compiler name if it is in the PATH.
  
  
  -- Configuring incomplete, errors occurred!
  See also "C:/Go/src/github.com/cloudson/gitql/libgit2/CMakeFiles/CMakeOutput.log".
  See also "C:/Go/src/github.com/cloudson/gitql/libgit2/CMakeFiles/CMakeError.log".
  make: *** [prepare] B▒▒d 1
  </code></pre>
  
  <p>So I've tried to point to gcc from mingw using:</p>
  
  <pre><code>export CC=/c/MinGW/bin/gcc.exe
  </code></pre>
  
  <p>and when I run make I get this error:</p>
  
  <pre><code>-- Check for working C compiler: C:/MinGW/bin/gcc.exe
  CMake Error: Generator: execution of make failed. Make command was: "nmake" "/NOLOGO" "cmTC_14ff0\fast"
  -- Check for working C compiler: C:/MinGW/bin/gcc.exe -- broken
  CMake Error at C:/Program Files/CMake/share/cmake-3.7/Modules/CMakeTestCCompiler.cmake:51 (message):
    The C compiler "C:/MinGW/bin/gcc.exe" is not able to compile a simple test
    program.
  
    It fails with the following output:
  
     Change Dir: C:/Go/src/github.com/cloudson/gitql/libgit2/CMakeFiles/CMakeTmp
  
  
  
    Run Build Command:"nmake" "/NOLOGO" "cmTC_14ff0\fast"
  
  
  
    Generator: execution of make failed.  Make command was: "nmake" "/NOLOGO"
    "cmTC_14ff0\fast"
  
  
  
  
  
    CMake will not be able to correctly generate this project.
  Call Stack (most recent call first):
    CMakeLists.txt:14 (PROJECT)
  
  
  -- Configuring incomplete, errors occurred!
  See also "C:/Go/src/github.com/cloudson/gitql/libgit2/CMakeFiles/CMakeOutput.log".
  See also "C:/Go/src/github.com/cloudson/gitql/libgit2/CMakeFiles/CMakeError.log".
  make: *** [prepare] B▒▒d 1
  </code></pre>
  
  <p>How can I inform cmake to use make instead of nmake? I have make installed in <code>C:\Program Files (x86)\GnuWin32\bin</code> which is in <code>$PATH</code>.</p>
  
  <p>I've also try to call <code>cmake -G "MinGW Makefiles"</code> but I've got this error:</p>
  
  <pre><code>CMake Error: The source directory "C:/Go/src/github.com/cloudson/gitql" does not appear to contain CMakeLists.txt.
  Specify --help for usage, or press the help button on the CMake GUI.
  </code></pre>