More traditional fallout

[Zack Weinberg]

> As require_constant_value is what is usually passed to
> require_constant and require_constant_elements usually passed to
> constructor_constants and from similarities in both error messages,
> I think either at some time digest_init used constructor_constant instead
> of require_constant together with initializer_constant_valid_p, or
> it ought to but never did actually.

I feel this isn't a productive line of analysis.  We ought to figure
out what sorts of warnings _should_ issue from this code, and make
that happen, rather than trying to deduce the meaning of some
long-forgotten and unused parameter.

This is the sort of thing that C conformance suites go over in detail;
Jakub, you have access to some of those, right?

zw