[Bug driver/115698] @file invalidates -B in g++ command line

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115698

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
So I looked into the driver code and '@' handling is early on and just expands
into the new arguments.