Created attachment 227736 [details]
msgpack 4.0.0 completely separates C and CXX, with separate distfiles. The CXX package is header-only and requires boost.
It's not totally clear to me which ports will want C vs CXX, so I figure a limited exp-run might be the easiest path. The attached patch switches things to msgpack-c; if they fail to build, they probably wanted CXX.
The msgpack line has to be removed from devel/Makefile
And a msgpack-c line has to be added
Some new failure logs: