Revisit -no-console option for Windows

The reason for ShowWindow opose to your FreeConsole is because if you start up
cmd.exe and do syncthing.exe -no-output it actually hides the existing cmd.exe
window oppose to opening a separate window and then hiding it, which keeps the
existing console hanging on syncthing.exe running.

I tried playing around with compiling as GUI, then given the option is not present
allocating a console, and redirecting the std streams to the new console, but that
seems ugly as I'd have to make quite a few calls. But that does get of the initial
flash.

internal/osutil/hidden_windows.go

@@ -48,3 +48,14 @@ func ShowFile(path string) error {
 	attrs &^= syscall.FILE_ATTRIBUTE_HIDDEN
 	return syscall.SetFileAttributes(p, attrs)
 }
+
+func HideConsole() {
+	getConsoleWindow := syscall.NewLazyDLL("kernel32.dll").NewProc("GetConsoleWindow")
+	showWindow := syscall.NewLazyDLL("user32.dll").NewProc("ShowWindow")
+	if getConsoleWindow.Find() == nil && showWindow.Find() == nil {
+		hwnd, _, _ := getConsoleWindow.Call()
+		if hwnd != 0 {
+			showWindow.Call(hwnd, 0)
+		}
+	}
+}