title: CMake : add_executable not generating an executable under windows OS
body: <p>I am trying to generate an executable with CMake under windows by command line.</p>
  
  <p>This is what I do: 
  I enter testprog directory then do</p>
  
  <pre><code> cd build
   cmake ..
  </code></pre>
  
  <p>I also tried this:</p>
  
  <pre><code>cd build
  cmake -G"Visual Studio 16 2019" ..
  </code></pre>
  
  <p>same result as earlier attempt.</p>
  
  <p>This builds bunch of files in build directory but no executable is ever created.
  It creates files to be opened in visual studio.</p>
  
  <p>This is how my folder look like;</p>
  
  <pre><code>testprog
        -build
        -src
               -main.cpp
               -call.h
        -include
              -main.h
              -call.h
        -CMakeLists.txt
  </code></pre>
  
  <p>CMakeLists.txt</p>
  
  <pre><code>cmake_minimum_required(VERSION 3.10)
  
  set(CMAKE_CXX_STANDARD 17)
  
  project(testprog)
  
  include_directories(include)
  
  file(GLOB SOURCES "src/*.cpp")
  
  add_executable(testprog ${SOURCES})
  </code></pre>