"What's the proper way to ask macports if it's installed and where to look for libraries/include headers?"

[John Douglas Owens via macports-dev]

Would someone consider answering this on 
https://github.com/pikepdf/pikepdf/issues/322 ? The proximate issue is that 
pikepdf assumes Homebrew is installed and the install breaks on MacPorts if 
Homebrew is not installed. The developer would like to fix this!

Thanks.

JDO