I don't think an input thread can ever be useful on Windows.

There is a pthread emulation, so having the thread itself isn't much of
a problem.

However, there is no device to wait on for Windows events, and even if
we were to replace select() with WFMO, Windows wants to send events for
a window to the thread which created that window.

So, disable input thread by default for MinGW

v2:
Also add similar to meson.build