[Bug fortran/93736] Add .f18 and .F18 file suffixes

[dominiq at lps dot ens.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93736

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

           What    |Removed                     |Added
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     Ever confirmed|0                           |1
   Last reconfirmed|                            |2020-07-12
             Status|UNCONFIRMED                 |NEW