New comment by sgn on void-packages repository

https://github.com/void-linux/void-packages/issues/46959#issuecomment-1786419379

Comment:
```
The reason for the non-prototype declaration is explained in commit
37bb3cce4598c19288628e675eaf1cda6e96958f:

    omit declaration of basename wrongly interpreted as prototype in C++

    the non-prototype declaration of basename in string.h is an ugly
    compromise to avoid breaking 2 types of broken software:

    1. programs which assume basename is declared in string.h and thus
    would suffer from dangerous pointer-truncation if an implicit
    declaration were used.

    2. programs which include string.h with _GNU_SOURCE defined but then
    declare their own prototype for basename using the incorrect GNU
    signature for the function (which would clash with a correct
    prototype).
```

So, we move `basename` to `#ifdef __cplusplus`?