FindBoost.cmake requires listing the system component in the find_package call
The note at the beginning of the FindBoost.cmake
says:
Implicit dependencies such as Boost::filesystem requiring Boost::system will be automatically detected and satisfied, even if system is not specified when using find_package and if Boost::system is not added to target_link_libraries.
But it is not the case with cmake 3.14.1, the behaviour has changed probably between 3.14 and 3.14.1. As of 3.14.1 listing the system component in the find_package()
call is required.