I blew a lot of time fooling with msys2/mingw-w64.

Short version: More Posix-like than MSys/Mingw32, and the package
manager pacman is great, but it is too Posix-like to work without
fixing many many things in the code. The liblo library used by OSC was
a particular problem; liblo's configure script wanted to use WIndows
sockets even though msys2/mingw-w64 provides Posix sockets.

I've switched back to 32 bit CPU architecture using MSys and the Qt
SDK's Mingw32 4.9.2.

There's still a lot to do...

Regards,
Mike

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Michael Gogins
Irreducible Productions
http://michaelgogins.tumblr.com