Looks similar to #597 with regard to Asio.

System and build information attached.

The build is successful with CPP-NETLIB_BUILD_SHARED_LIBS=OFF though we are also seeing similar errors upon linking with Kovri which is preventing us from providing official MinGW support (note: the Linux/OSX builds are successful with the same options).

@deanberris I too don't use Windows or MinGW but have recently had to for the Kovri build so, if there is a simple solution then I hope someone reading this can pass on the wisdom.