[Bug c/65403] -Wno-error=<not implemented> is an error

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65403

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Besides that the error also complains about -Werror= instead of -Wno-error=