Well the real error is actually:
:info:configure Expat must be installed prior to building XML::Parser and I can't find
:info:configure it in the standard library directories. Install 'expat-devel' (or
:info:configure 'libexpat1-dev') package with your OS package manager. See 'README'.
But as Jeff points out, expat is, of course, already installed.
I don't see this problem on my High Sierra system with Xcode 9.4.1.
It could certainly relate to Xcode 11, as you say, Frank.
I don't suppose perl writes anything like a config.log file anywhere to tell us what exactly went wrong? Possibly inside the directory /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_perl_p5-xml-parser/p5.28-xml-parser/work/XML-Parser-2.46?