So there seems to be an issue with util/processinfo_darwin.cpp as described in MacPorts trac
I'm stuggling to find the file to edit? any help?
from here: https://svn.macports.org/ticket/30263 as Jan mentioned above
sudo port clean mongodb
sudo port extract mongodb
cd $(port work mongodb)/mongodb*
sudo curl -O https://jira.mongodb.org/secure/attachment/12395/lion.patch
sudo patch -p1 < lion.patch
cd
sudo port install mongodb