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

fusl/src/time/mktime.c

+#include "time_impl.h"
+#include <errno.h>
+
+time_t mktime(struct tm *tm)
+{
+        struct tm new;
+        long opp;
+        long long t = __tm_to_secs(tm);
+
+        __secs_to_zone(t, 1, &new.tm_isdst, &new.__tm_gmtoff, &opp, &new.__tm_zone);
+
+        if (tm->tm_isdst>=0 && new.tm_isdst!=tm->tm_isdst)
+                t -= opp - new.__tm_gmtoff;
+
+        t -= new.__tm_gmtoff;
+        if ((time_t)t != t) goto error;
+
+        __secs_to_zone(t, 0, &new.tm_isdst, &new.__tm_gmtoff, &opp, &new.__tm_zone);
+
+        if (__secs_to_tm(t + new.__tm_gmtoff, &new) < 0) goto error;
+
+        *tm = new;
+        return t;
+
+error:
+        errno = EOVERFLOW;
+        return -1;
+}