[Bug c/86134] earlier diagnostic causes followup diagnostic about unknown -Wno-* options

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86134

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
As per the recent discussion:
https://gcc.gnu.org/ml/gcc-patches/2018-06/msg00422.html