Use GDI mode for Windows builds of SCFG, making this a Windows/GUI app now

In Windows 11, "Windows Terminal" is now the default console (though the
Windows user can change that to the old conhost.exe).  Running UIFC
apps (e.g. SCFG) in Windows console mode from within a Windows Terminal
console doesn't always display correctly (depending on the width of the
console). And even if if the app displays correctly at first in console
mode, it's very easy for the user to resize the console window and just
totally foobar the display of the app.

Windows console mode (previously, the default interface mode) is still
available ("-iw" option) if one wants to use it instead.

However, stdio/door mode ("-id") and ANSI mode ("-ia") can't be used directly
from a console.

The help/usage output is sent in Windows console mode (not stdout or GDI mode)
so it creates a new window, disables mouse support (so you can copy text from
it). stdout doesn't work from GUI apps. Fun times.