Fix #issue 23177 - add a diagnostic hint for f() vs f(void)

[gulugulubing]

It is related to #23177: Add a ParamListMismatchHint() in importc.d for the case: parameter is K&R (), argument is a prototyped empty list, and toChars() match.

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[dkorpel]

This is too much code just to address the problem in a very specific case. As a simpler solution, perhaps add a new string representation for K&R variadics in hdrgen.d, so that it doesn't print as: void function() but as void function(<K&R variadics>) (there is not syntax for this in D so it doesn't have to compile) . That should clarify the mismatch in all cases.

[gulugulubing]

As a simpler solution, perhaps add a new string representation for K&R variadics in hdrgen.d, so that it doesn't print as: void function() but as void function(<K&R variadics>)

Got it. It's nicer.

[dkorpel]

Why !pl.length?

[gulugulubing]

Should be removed. And I added a test with one parameter.

[ntrel]

Another option: "<unspecified>".

[ntrel]

Given C23 allows ... without a named parameter (see #23232), perhaps we can just use ... for this.

[gulugulubing]

Thanks for the help.