There are two main subsystems under Windows. The CONSOLE subsystem
(which is the default subsystem) will always create a console when
launching the application. This is not something desirable when the
application has a Windows GUI. To get rid of this console the
application must be using the WINDOWS subsystem. To do so
the -mwindows linker option must be specified.
$ gnatmake winprog -largs -mwindows