[Bug fortran/54687] Use gcc option machinery for gfortran

[manu at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54687

Manuel López-Ibáñez <manu at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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             Status|WAITING                     |NEW

--- Comment #12 from Manuel López-Ibáñez <manu at gcc dot gnu.org> ---
(In reply to Dominique d'Humieres from comment #11)
> What is left in this PR before closing it as FIXED?

My understanding is that almost all entries in gfc_option_t are duplicated in
the common machinery (and if not, that would be quite strange and possibly
buggy, or just they are not command-line options, so why they reside in
gfc_option_t?).

My intuition is that almost all the code in gfc_handle_option can be generated
automatically by using the appropriate flags in fortran/lang.opt
(https://gcc.gnu.org/onlinedocs/gccint/Option-properties.html). But that could 
be done incrementally apart from this bug.

There are some things that both the common machinery and Fortran do manually
(PR64334). Factoring out that code (possibly generating it automatically from
the .opt files) would be nice, but not essential (so PR64334 does not actually
block this).