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

[thenlich at gcc dot gnu.org]

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

--- Comment #6 from Thomas Henlich <thenlich at gcc dot gnu.org> ---
Created attachment 47842
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47842&action=edit
Proposed patch to add .f18/.F18 suffix

Add .f18 and .F18 to list of recognized filename suffixes to match the most
recent standard Fortran 2018