[m-rev.] for post-commit review: store env var maps in options_variables

[Julien Fischer]

On Mon, 30 Aug 2021, Zoltan Somogyi wrote:

> For review by Julien.

> Include environment vars in options_variables.
> 
> compiler/options_file.m:
>     As above. This allows all lookup operations on options_variables
>     to stop requiring access to the I/O state.
> 
> compiler/make.build.m:
> compiler/make.m:
> compiler/make.program_target.m:
>     Stop passing now-unneeded I/O state pairs.
> 
> compiler/mercury_compile_main.m:
>     Stop passing now-unneeded I/O state pairs.
>
>     Do pass the complete environment variable map to the function
>     that initializes options_variables.

That looks fine.

Julien.