title: Compile error when std::filesystem header file is added to my program
body: <p>I am trying to compile a simple C++ program with std::filesytem header file included!</p>
  
  <pre><code>#include &lt;iostream&gt;
  #include &lt;filesystem&gt;
  
  int main() {
      std::cout &lt;&lt; "Hello, World!" &lt;&lt; std::endl;
      return 0;
  }
  </code></pre>
  
  <p>On compiling I get the following error</p>
  
  <pre><code>In file included from C:/PROGRA~1/MINGW-~1/X86_64~2.0-W/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/filesystem:37,
                   from C:\Users\{User}\CLionProjects\untitled3\main.cpp:2:
  C:/PROGRA~1/MINGW-~1/X86_64~2.0-W/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/fs_path.h: In member function 'std::filesystem::__cxx11::path&amp; std::filesystem::__cxx11::path::operator/=(const std::filesystem::__cxx11::path&amp;)':
  C:/PROGRA~1/MINGW-~1/X86_64~2.0-W/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/fs_path.h:237:47: error: no match for 'operator!=' (operand types are 'std::filesystem::__cxx11::path' and 'std::filesystem::__cxx11::path')
      || (__p.has_root_name() &amp;&amp; __p.root_name() != root_name()))
                                 ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~
  </code></pre>
  
  <p>I am on windows OS using MingW 8.1.0 and Clion as the IDE
  and as depicted on this <a href="https://en.cppreference.com/w/cpp/compiler_support" rel="nofollow noreferrer">https://en.cppreference.com/w/cpp/compiler_support</a> seems like GCC 8.1 already supports std:fileystem</p>
  
  <p><a href="https://i.stack.imgur.com/SdcKv.png" rel="nofollow noreferrer">ToolChain config</a></p>
  
  <p>EDIT:
  Language level is set in my CMakeList as shown below</p>
  
  <pre><code>set(CMAKE_CXX_STANDARD 17)
  </code></pre>