4.2 Project: "@file" support

[DJ Delorie]

> FWIW, I should note that GCJ already has support for @file
> style list of input files:
> 
>   http://gcc.gnu.org/onlinedocs/gcj/Input-and-output-files.html
> 
> and has had it for quite some time now.

DJGPP and Cygwin hosted programs will never see these options, because
the runtime has already expanded them if appropriate.

Which means your documentation is *wrong* for those platforms; for
them, *any* command line option is legal in @file.  Please update your
documentation ;-)