I found this by running "make test" on musl build of Python.

$ cat test_asctime.c
#include <time.h>
#include <stdio.h>

int main()
{
    char *c = asctime(0);
    printf("After asctime\n");
    if (c) printf("c=%s", c);
}
$ gcc test_asctime.c   -o test_asctime
$ test_asctime
After asctime
$ musl-gcc test_asctime.c   -o test_asctime
$ test_asctime
Segmentation fault (core dumped)
$