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

fusl/src/string/stpcpy.c

+#include <string.h>
+#include <stdint.h>
+#include <limits.h>
+#include "libc.h"
+
+#define ALIGN (sizeof(size_t))
+#define ONES ((size_t)-1/UCHAR_MAX)
+#define HIGHS (ONES * (UCHAR_MAX/2+1))
+#define HASZERO(x) ((x)-ONES & ~(x) & HIGHS)
+
+char *__stpcpy(char *restrict d, const char *restrict s)
+{
+        size_t *wd;
+        const size_t *ws;
+
+        if ((uintptr_t)s % ALIGN == (uintptr_t)d % ALIGN) {
+                for (; (uintptr_t)s % ALIGN; s++, d++)
+                        if (!(*d=*s)) return d;
+                wd=(void *)d; ws=(const void *)s;
+                for (; !HASZERO(*ws); *wd++ = *ws++);
+                d=(void *)wd; s=(const void *)ws;
+        }
+        for (; (*d=*s); s++, d++);
+
+        return d;
+}
+
+weak_alias(__stpcpy, stpcpy);