title: Can't find package X11 on WSL
body: <p>I'm trying to build an opensource project on WSL using cmake.
  I'm getting first these two errors which I don't understand : </p>
  
  <pre><code>CMake Error at /usr/share/cmake-3.16/Modules/CMakeDetermineSystem.cmake:185 (configure_file):
   configure_file Problem configuring file
  Call Stack (most recent call first):
   CMakeLists.txt:2 (project)
  
  The CXX compiler identification is GNU 9.3.0
  CMake Error at /usr/share/cmake-3.16/Modules/CMakeDetermineCXXCompiler.cmake:210 (configure_file):
   configure_file Problem configuring file
  Call Stack (most recent call first):
   CMakeLists.txt:2 (project)
  </code></pre>
  
  <p>and for X11:</p>
  
  <pre><code>Searching X11
  CMake Error at /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:146 (message):
  Could NOT find X11 (missing: X11_X11_LIB)
  Call Stack (most recent call first):
   /usr/share/cmake-3.16/Modules/FindPackageHandleStandardArgs.cmake:393 (_FPHSA_FAILURE_MESSAGE)
   /usr/share/cmake-3.16/Modules/FindX11.cmake:366 (find_package_handle_standard_args)
   CMakeLists.txt:18 (FIND_PACKAGE)
  </code></pre>
  
  <p>Here is the cmakelist.txt provided : </p>
  
  <pre><code>#CMake for the gard Project
  project(GARD)
  
  cmake_minimum_required(VERSION 2.4.0)
  
  #Set the path to the Cmake Modules
  SET(CMAKE_MODULE_PATH "${CMAKE_SOURCE_DIR}/cmake_modules/")
  MESSAGE("Path to Cmake Modules is " ${CMAKE_MODULE_PATH})
  
  MESSAGE("The source directory of the project is " ${GARD_SOURCE_DIR})
  
  
  MESSAGE("")
  MESSAGE("STEP 1 : SEARCHING FOR NEEDED MODULES")
  MESSAGE("")
  
  MESSAGE("Searching X11")
  FIND_PACKAGE(X11 REQUIRED)
  IF(X11_FOUND)
      MESSAGE(" X11 include path: " ${X11_INCLUDE_DIR})
      MESSAGE(" X11 library path: " ${X11_LIBRARIES})
  ENDIF(X11_FOUND)
  
  MESSAGE("Searching LAPACK AND BLAS")
  find_package(LAPACK)
  IF(LAPACK_FOUND)
      MESSAGE(" LAPACK library path: " ${LAPACK_LIBRARIES})
      MESSAGE(" BLAS library path: " ${BLAS_LIBRARIES})
  ENDIF(LAPACK_FOUND)
  
  MESSAGE("Searching CIMG")
  find_package(CImg)
  IF(CIMG_FOUND)
      MESSAGE(" CIMG include path: " ${CIMG_INCLUDE_DIR})
  ENDIF(CIMG_FOUND)
  
  MESSAGE("Searching pthread")
  FIND_LIBRARY(PTHREADS_LIBRARY pthread
    PATHS /usr/local/lib /usr/lib /usr/lib/x86_64-linux-gnu
    )
  IF(PTHREADS_LIBRARY)
      MESSAGE(" Pthread library path: " ${PTHREADS_LIBRARY})
  ENDIF(PTHREADS_LIBRARY)
  
  MESSAGE("Searching Graphviz")
  find_package(GraphViz)
  IF(GRAPHVIZ_FOUND)
      MESSAGE(" Graphviz library path: " ${GRAPHVIZ_LIBRARIES})
      MESSAGE(" Graphviz include path: " ${GRAPHVIZ_INCLUDE_DIRS})
      SET(GRAPHVIZ_SUPPORT "#define GRAPHVIZ_SUPPORT")
  ENDIF(GRAPHVIZ_FOUND)
  
  CONFIGURE_FILE(GraphVizConfig.h.cmake ${CMAKE_SOURCE_DIR}/include/core/GraphVizConfig.h) 
  
  find_package(OpenMP)
  if(OPENMP_FOUND)
      message("openMP found")
      set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
      set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
  endif()
  
  MESSAGE("Searching FLANN")
  find_package(Flann)
  IF(FLANN_FOUND)
      MESSAGE(" FLANN include path: " ${FLANN_INCLUDE_DIR})
      include_directories(${FLANN_INCLUDE_DIR})
      SET(FLANN_SUPPORT "#define FLANN_SUPPORT")
  ELSE(FLANN_FOUND)
      MESSAGE(" FLANN include path not found")
      SET(FLANN_SUPPORT "")
  ENDIF(FLANN_FOUND)
  
  include(ProcessorCount)
  ProcessorCount(N)
  
  if(NOT N EQUAL 0)
      set(AVAILABLE_CORES "#define AVAILABLE_CORES ${N}")
  else(NOT N EQUAL 0)
      set(AVAILABLE_CORES "#define AVAILABLE_CORES 1")
  endif()
  
  CONFIGURE_FILE(FlannConfig.h.cmake ${CMAKE_SOURCE_DIR}/include/core/FlannConfig.h)
  
  MESSAGE("")
  
  MESSAGE("")
  MESSAGE("STEP 2 : SET INCLUDE AND LIBRARY PATHS")
  MESSAGE("")
  SET(GARD_INCLUDE_DIR    ${GARD_SOURCE_DIR}/include)
  
  
  IF(LAPACK_FOUND)
      SET(LINK_LIBRARIES ${X11_LIBRARIES} ${PTHREADS_LIBRARY} ${LAPACK_LIBRARIES} ${BLAS_LIBRARIES} ${GRAPHVIZ_LIBRARIES})
      SET(CIMG_USE_LAPACK "#define cimg_use_lapack")
  ELSE()
      SET(LINK_LIBRARIES ${X11_LIBRARIES} ${PTHREADS_LIBRARY} ${GRAPHVIZ_LIBRARIES})
  ENDIF()
  
  CONFIGURE_FILE(CimgConfig.h.cmake ${CMAKE_SOURCE_DIR}/include/core/CimgConfig.h)
  
  MESSAGE("")
  MESSAGE("STEP 3 : Documentation generation")
  MESSAGE("")
  
  MESSAGE("Searching DOXYGEN")
  INCLUDE(${CMAKE_MODULE_PATH}/FindDoxygen.cmake)
  IF(DOXYGEN_FOUND)
      MESSAGE("DOXYGEN Dir " ${DOXYGEN_DIR})
      MESSAGE("GENERATING DOCUMENTATION")
      SET(ENV{GARD_INCLUDE_DIR} "${GARD_SOURCE_DIR}/include")
      EXEC_PROGRAM("cd docs;${DOXYGEN_DIR}/doxygen doc.txt"
      OUTPUT_VARIABLE MY_OUTPUT
      )
  ENDIF(DOXYGEN_FOUND)
  
  MESSAGE(STATUS "Link libraries:  ${LINK_LIBRARIES}")
  
  
  MESSAGE("")
  MESSAGE("STEP 4 : COMPILATION")
  MESSAGE("")
  
  
  add_subdirectory (${GARD_SOURCE_DIR}/examples)
  # add_subdirectory (${GARD_SOURCE_DIR}/operators)
  </code></pre>
  
  <p>Can you help please? I'm new to cmake and WSL. I'm running WSL on Windows 10 and I've installed the X11 library with " sudo apt-get install libx11-dev "  . The command 'cmake .' is running in the bash terminal and looks like : </p>
  
  <pre><code>ananass@DESKTOP-R1E6G2S:/mnt/c/Users/ananass/gard$
  </code></pre>