[RFC] Consider adding a function to convert error name to errno

[Florian Weimer]

* Rocket Ma:

>> POSIX 2024 added something for signals [1], so maybe we can go to follow
>> strerrorname_np:
>>
>>   int strnameerror_np (const char *restrict str, int *restrict errnum);
>
> Wait, if the `str' in `strerror' means the return type is `str', then
> should we name the function `intnameerror_np'?

The prefix “str” makes the name reserved.  We have function like strtod
that produce non-string results.

Thanks,
Florian