[m-rev.] for post-commit review: improve const_prop.m

[Julien Fischer]

On Mon, 17 Apr 2023, Zoltan Somogyi wrote:

> Small improvements in the code simplifying calls.
> 
> compiler/const_prop.m:
>     Replace pairs and maybes with a semantically meaningful type.
>     Restrict this type to the part we actually use.
>
>     Optimize ubits_per_{int,uint} the same way we have long optimized
>     bits_per_{int,uint}.
> 
> compiler/simplify_goal_call.m:
>     Improve the wording of some warnings.
>
>     When constructing those warnings, don't test the value of warn_simple_code
>     twice.
> 
> compiler/uint_emu.m:
>     Fix copy-and-paste typo.
> 
> tests/warnings/unsigned_zero_cmp.exp:
>     Expect the updated text of the above warnings.

That's fine.

Julien.