I have tried the 2 most sane-looking of them:
-- sudo /usr/bin/xcode-select -switch /Applications/Xcode.app
(interesting that after this, xcode-select -print-path shows
--and changing developer_dir in macports.conf to
With this, I can now install at least some ports without any warning. I
have found a problem in for example libvpx, but I am not sure if this is a
problem in the port itself.
Note, I am using ccache and parallel builds, so my environment might be
more demanding than "normal".