Auto merge of #6122 - ehuss:msys-width, r=alexcrichton

Second attempt at fixing msys terminal width.

Lock the max width on msys-based terminals to 60. I tried a lot of different
things, but I was unable to find a way to detect the correct width in mintty.
Unfortunately this means that terminals that work correctly like ConEmu will
also be capped at 60. C'est la vie.

Of course this does not affect cmd, powershell, etc.

Fixes #6108