Boost process requires linking Boost filesystem

[luxean]

Although Boost process is header only, it requires linking with Boost filesystem on Windows. There seems to be a workaround using the preprocessor definition BOOST_PROCESS_USE_STD_FS. Unfortunately, that still leads to some compilation errors with the Boost process library. Tested with Visual Studio 2019 and Boost 1.80. Might be fixed by using a newer release of Visual Studio (2022) or Boost version (1.81).