Make sure that the preprocessor directive in 'winmain.cc' matches the one in 'main.cc'

(also, some minor housekeeping)
Add some stuff that's needed for an MSVC built target:-

1) Make sure we create or open any files in binary mode
2) Make sure the user can see an error message of we fail to parse the command line
3) Make sure that the call to 'windows_vst_gui_init()' matches its declaration (i.e. only applicable when NOT on PLATFORM_WINDOWS)