[Bug other/69821] -fdebug-prefix-map doesn't affect gcc command line switches in DWARF DW_AT_producer.

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69821

--- Comment #7 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
It is not a regression and is user visible change, so I think changing it just
in GCC 6 is sufficient.