Fail to use self build Boost 1.75 under Ubuntu Linux 20.04 x64 with CMake default and 3.19.4

For reference, CMake 3.19.5 will update FindBoost to be aware of Boost 1.75. See CMake Issue 21773.

See CMake Issue 17701 about the layout differences.

However, Boost upstream now provides a proper CMake package file BoostConfig.cmake which should work for using Boost in any layout.