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

[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'?