title: CMake toolchain includes multiple files
body: <p>For the reasons irrelevant to mention I would like to be able to include multiple files into toolchain file. Let's say my toolchain contains following:</p>
  
  <pre>
  message(STATUS "file1 is ok")
  include(./build/file2)
  </pre>
  
  <p>the file2 contains identification line:</p>
  
  <pre>
  message(STATUS "file2 is ok")
  </pre>
  
  <p>the CMakeLists.txt contains:<pre>
  cmake_minimum_required (VERSION 2.8.8)
  project (pro)
  message(STATUS "cmakelists.txt is ok")</pre></p>
  
  <p>I call it using following command:<pre>
  cmake -DCMAKE_TOOLCHAIN_FILE=../../build/file1 ../../</pre></p>
  
  <p>Now, I would expect the following output:<pre>
  -- file1 is ok
  -- file2 is ok
  -- cmakelists.txt is ok</pre></p>
  
  <p>Yet I get this:<pre>
  -- file1 is ok
  -- file2 is ok
  -- file1 is ok
  -- file2 is ok
  -- The C compiler identification is Clang 5.0.0
  -- The CXX compiler identification is Clang 5.0.0
  -- Check for working C compiler: /usr/bin/cc
  CMake Error at /fullpath/build/file1:2 (include):
    include could not find load file:
      ./build/file2
  Call Stack (most recent call first):
    /fullpath/build/Mac/CMakeFiles/2.8.12/CMakeSystem.cmake:6 (include)
    CMakeLists.txt:2 (PROJECT)
  CMake Error: Internal CMake error, TryCompile configure of cmake failed
  -- Check for working C compiler: /usr/bin/cc -- broken
  CMake Error at /Applications/CMake 2.8-12.app/Contents/share/cmake-2.8/Modules/CMakeTestCCompiler.cmake:61 (message):
    The C compiler "/usr/bin/cc" is not able to compile a simple test program.
    It fails with the following output:
    CMake will not be able to correctly generate this project.
  Call Stack (most recent call first):
    CMakeLists.txt:2 (project)
  -- Configuring incomplete, errors occurred!</pre></p>
  
  <p>Not only does CMake print the information twice, it also claim it cannot find included files at third time after that.</p>
  
  <p>Any ideas?</p>