title: Error in building Assimp in Cmake
body: <p>Hi I'm trying to build Assimp with Cmake but the following error message appears everytime I try to configure Assimp. The version of Cmake is 3.11.0 and assimp is 4.0.0.</p>
  
  <pre><code>Looking for DirectX...
  DirectX_PREFIX_PATH changed.
  Found DirectX: C:/Program Files (x86)/Microsoft DirectX SDK (June 2010)/Lib/x86/d3d9.lib
  DX lib dir: C:/Program Files (x86)/Microsoft DirectX SDK (June 2010)/Lib/x86
  Looking for ZLIB...
  Found PkgConfig: C:/cygwin/bin/pkg-config.exe (found version "0.29.1") 
  Checking for module 'zzip-zlib-config'
    No package 'zzip-zlib-config' found
  Could not locate ZLIB
  compiling zlib from sources
  CMake Deprecation Warning at contrib/zlib/CMakeLists.txt:8 (cmake_policy):
    The OLD behavior for policy CMP0048 will be removed from a future version
    of CMake.
  
    The cmake-policies(7) manual explains that the OLD behaviors of all
    policies are deprecated and that a policy should be set to OLD only under
    specific short-term circumstances.  Projects should be ported to the NEW
    behavior and not rely on setting a policy to OLD.
  
  
  Looking for sys/types.h
  Looking for sys/types.h - found
  Looking for stdint.h
  Looking for stdint.h - found
  Looking for stddef.h
  Looking for stddef.h - found
  Check size of off64_t
  Check size of off64_t - failed
  Looking for fseeko
  Looking for fseeko - not found
  Looking for unistd.h
  Looking for unistd.h - not found
  Could NOT find rt (missing: RT_LIBRARY) 
  Enabled formats: AMF 3DS AC ASE ASSBIN ASSXML B3D BVH COLLADA DXF CSM HMP IRRMESH IRR LWO LWS MD2 MD3 MD5 MDC MDL NFF NDO OFF OBJ OGRE OPENGEX PLY MS3D COB BLEND IFC XGL FBX Q3D Q3BSP RAW SIB SMD STL TERRAGEN 3D X X3D GLTF 3MF MMD
  Disabled formats:
  Looking for DirectX...
  DirectX_PREFIX_PATH changed.
  DX lib dir: C:/Program Files (x86)/Microsoft DirectX SDK (June 2010)/Lib/x86
  Could NOT find IL (missing: IL_LIBRARIES IL_INCLUDE_DIR) 
  CMake Error at C:/cygwin/lib/cmake/Qt5Gui/Qt5GuiConfig.cmake:27 (message):
    The imported target "Qt5::Gui" references the file
  
       "C:/cygwin/include/qt5/"
  
    but this file does not exist.  Possible reasons include:
  
    * The file was deleted, renamed, or moved to another location.
  
    * An install or uninstall procedure did not complete successfully.
  
    * The installation package was faulty and contained
  
       "C:/cygwin/lib/cmake/Qt5Gui/Qt5GuiConfig.cmake"
  
    but not all the files it references.
  
  Call Stack (most recent call first):
    C:/cygwin/lib/cmake/Qt5Gui/Qt5GuiConfig.cmake:68 (_qt5_Gui_check_file_exists)
    C:/cygwin/lib/cmake/Qt5/Qt5Config.cmake:28 (find_package)
    tools/assimp_qt_viewer/CMakeLists.txt:19 (FIND_PACKAGE)
  
  
  Configuring incomplete, errors occurred!
  See also "C:/Users/peter/Desktop/assimp-master/assimp-master/build/CMakeFiles/CMakeOutput.log".
  See also "C:/Users/peter/Desktop/assimp-master/assimp-master/build/CMakeFiles/CMakeError.log".
  </code></pre>
  
  <p>For the configuration generator I used Visual Studio 15 2017 since I'm using that for my IDE. Is there anyway that this can be solved?</p>