[boost] [CMake] Can/should we specify optional dependencies

I have a regex bug report relating to linking to ICU when using CMake: https://github.com/boostorg/regex/issues/143 Is there a correct way to specify in the CMake file that if you use header X, then you should also link to library Y, but otherwise not? Thanks, John. -- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus