Avoid spinner on Windows

Fixes #4147, probably.

## Verification

 - [x] Start `./msfconsole -L` on a non-Windows system, and amaze at the hypnotic beauty of the spinner.
 - [x] Start `./msfconsole -L` on a Windows system, and feel the cold emptiness of its absence wash over you.
  - [x] Ditto for an undecorated `./msfconsole` start of the MSF console.