[Bug fortran/79854] diagnostics: gfc_conv_constant_to_tree should be gfc_internal_error

[kargl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79854

kargl at gcc dot gnu.org changed:

           What    |Removed                     |Added
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                 CC|                            |kargl at gcc dot gnu.org

--- Comment #3 from kargl at gcc dot gnu.org ---
(In reply to Eric Gallager from comment #2)
> (In reply to Dominique d'Humieres from comment #1)
> > AFAICT this internal error has never triggered. If someone can come with a
> > test for it, this would be nice.
> 
> In the meantime, though, I think it'd make sense just to change it to an
> internal error anyways (even without a testcase), for translation purposes

Unless someone can trigger this error or can prove that gfc_internal_error
is available when the error ought to trigger, then please leave the
code as is.

fatal_error() is used in a number places because gfortran's error mechanism
is not available.  See gfc_init() and gfc_init_1().