title: How to specify CMAKE RUNTIME_OUTPUT_DIRECTORY correctly?
body: <p>I have the following directory structure</p>
  
  <pre><code>cmake_test
  ├── bin
  ├── CMakeLists.txt
  ├── src
  │   └── func.cxx
  └── subproj
      ├── CMakeLists.txt
      └── src
          └── main.cxx
  </code></pre>
  
  <p>CMakeLists.txt :</p>
  
  <pre><code>cmake_minimum_required(VERSION 2.8)
  
  project(main)
  
  set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_HOME_DIRECTORY}/bin/)
  set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_HOME_DIRECTORY}/bin/lib/)
  set(CMAKE_CXX_FLAGS_DEBUG "-std=c++11 -Wall -g3 -O0")
  set(CMAKE_CXX_FLAGS "-std=c++11 -Wall -Wextra")
  
  set(META_SRC_DIR ${CMAKE_HOME_DIRECTORY}/src)
  
  aux_source_directory(${META_SRC_DIR}/           META_SRC_LIST)
  
  add_subdirectory(subproj)
  </code></pre>
  
  <p>subproj/CMakeLists.txt :</p>
  
  <pre><code>cmake_minimum_required(VERSION 2.8)
  
  project(subproj)
  
  aux_source_directory(${PROJECT_SOURCE_DIR}/src  SRC_LIST)
  
  #include_directories(${PROJECT_SOURCE_DIR}/include)
  
  add_executable(${PROJECT_NAME} ${SRC_LIST})
  </code></pre>
  
  <p>When I build this project (<code>cd bin; cmake ..; make</code>) I face following error:</p>
  
  <pre><code>Scanning dependencies of target subproj
  [ 50%] Building CXX object subproj/CMakeFiles/subproj.dir/src/main.cxx.o
  [100%] Linking CXX executable .
  /usr/bin/ld: cannot open output file .: Is a directory
  collect2: error: ld returned 1 exit status
  subproj/CMakeFiles/subproj.dir/build.make:94: recipe for target 'subproj' failed
  make[2]: *** [subproj] Error 1
  CMakeFiles/Makefile2:85: recipe for target 'subproj/CMakeFiles/subproj.dir/all' failed
  make[1]: *** [subproj/CMakeFiles/subproj.dir/all] Error 2
  Makefile:83: recipe for target 'all' failed
  make: *** [all] Error 2
  </code></pre>
  
  <p>How to fix it?</p>