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This build works as well. I'm not sure what's wrong with my
local environment.

The version of mingw in Fedora 21 works as well.
This is the first version to depend on libwinpthread.

Also add an autogen.sh invocation which caused the previous
build to fail after the 'make check' barrier was removed.

For some reason, when I cross-compile opusfile on Fedora 23,
I get example binaries with exit immediately without error.

Building them on Fedora 20 (in a docker container) produced
working binaries. Until we figure out what the bug is, include
this for convenience.

The build doesn't actually work because of the 'make check'
steps in the Makefile, which require wine.