[Bug fortran/82018] -Wextra should imply -Wconversion-extra

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82018

Dominique d'Humieres <dominiq at lps dot ens.fr> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P5
           Severity|normal                      |enhancement

--- Comment #8 from Dominique d'Humieres <dominiq at lps dot ens.fr> ---
> Another alternative would be to have three flags:
> ...

Exactly what I feared in comment 4!-(the time taken by this PR is not devoted
to more important ones, e.g., final review for Paul's patch PR34640).