I ran into this issue while trying to install wine-devel on my Mid 2012 MacBook Pro running El Capitan and MacPorts 2.3.4. As the install progressed, here is the error I got:

Error: org.macports.build for port glib2 returned: command execution failed
Please see the log file for port glib2 for details:
    /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_devel_glib2/glib2/main.log
Error: Unable to upgrade port: 1
Error: Unable to execute port: upgrade gnutls failed

This appears to be a known bug with the MacPorts glib2 port. Commenters on that link suggest that re-installing sqlite3 with the +universal variant addresses the problem. Although this is a bit puzzling (the glib2 port owner seems to have fixed the problem), I decided to give it a go anyway. Lo and behold sudo port install sqlite3 +universal fixed the problem and let glib2 and wine install normally.

For the curious, I am installing wine to try out the Windows version of EVE Online. I have heard that running the Windows version in wine is better performing than the official Cider client. I will update later with my findings. If you are interested in trying EVE Online, here is a free 30 day trial.