[musl] perhaps we should add re[c]allocarray?

[Ariadne Conill <ariadne@dereferenced.org>]

Hello,

reallocarray and recallocarray are BSD extensions that solve similar issues as 
strlcpy/strlcat, but with array reallocations instead of strings.

reallocarray itself is already part of glibc since 2.28.

Unfortunately, while working on new ifupdown implementation for Alpine, I 
wanted to use recallocarray because it is very helpful in terms of pushing new 
strings to a string array (you will always maintain a NULL-terminated array, 
and you don't have to worry about it) -- but I discovered musl still does not 
have it.

Anyway, I think it would be useful to include both functions in musl 1.2.1.  
If everyone agrees, I'll make a patch.

Ariadne