Otherwise it would be possible to do e.g.

`pthread_mutex_t mutex = PTHREAD_ONCE_INITIALIZER;```,
which would expand to
```pthread_mutex_t mutex = {0};```.

close #165

close #32

reallocarray introduction available on glibc 2.26. allocates an array of m*n elements but checking for overflow.

close #164

those functions differently than the strn* ones as
they do not pad with zero to remaining bytes but guarantees
a null terminator.