Build Win32 /Core binaries as console mode applications

A console mode Rebol binary has the following advantages:

- Reuses an existing command prompt
- Works with alternative command prompts (such as Console 2)
- Slightly improves the handling of redirected standard IO

Until we reintegrate /View capabilities and/or a custom graphical
(R2-style) console, building console mode binaries is the better default
for Windows.