Add a "fork" of musl as //fusl.

fusl/src/time/localtime_r.c

+#include "time_impl.h"
+#include <errno.h>
+#include "libc.h"
+
+struct tm *__localtime_r(const time_t *restrict t, struct tm *restrict tm)
+{
+        /* Reject time_t values whose year would overflow int because
+         * __secs_to_zone cannot safely handle them. */
+        if (*t < INT_MIN * 31622400LL || *t > INT_MAX * 31622400LL) {
+                errno = EOVERFLOW;
+                return 0;
+        }
+        __secs_to_zone(*t, 0, &tm->tm_isdst, &tm->__tm_gmtoff, 0, &tm->__tm_zone);
+        if (__secs_to_tm((long long)*t + tm->__tm_gmtoff, tm) < 0) {
+                errno = EOVERFLOW;
+                return 0;
+        }
+        return tm;
+}
+
+weak_alias(__localtime_r, localtime_r);