RFC: patch to add ISO_FORTRAN_ENV intrinsic module

[FX Coudert]

> How about leaving it to e.g. 32 and spitting out a warning when one
> loads the module and has -fdefault-integer-8 XOR -fdefault- 
> integer-8 set.

I'll go for issuing a warning if -fdefault-integer-8 OR -fdefault- 
integer-8. After all, even when both flags are specified, chances are  
slim that the compiler is Standard compliant :)

As for the second part of my RFC, I'd very much like some advice.  
Paul, would you have a few minutes? Here's my question:

>  -- I've used the attr.intrinsic bit for the module symbol to
> specifiy that it's an intrinsic module. Except one line in resolve.c
> (see diff), it seems to be safe. However, I'd like
>    a) to be sure that, for every user module symbol created, the
> intrinsic bit is set to 0, so that we check that a non-intrinsic and
> an intrinsic module of the same name aren't used
>    b) the code USEing non-intrinsic modules (in module.c) to issue an
> error if an intrinsic module of the same name was already USEd; ie,
> I'd like the following to error out (while, with my patch, it does
> not):
>
> module iso_fortran_env
> end module iso_fortran_env
>
> program foo
>  use, intrinsic :: iso_fortran_env
>  use, non_intrinsic :: iso_fortran_env ! This should issue an error
> end program foo

Thanks all,
FX