[Bug c/67665] ICE when passing two empty files directly to cc1 with -g

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67665

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For C++ we produce:
foo.c:1:0: fatal error: inter-module optimizations not implemented for C++

but really this should also be done for C now too.