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

fusl/src/string/memmove.c

+#include <string.h>
+#include <stdint.h>
+
+#define WT size_t
+#define WS (sizeof(WT))
+
+void *memmove(void *dest, const void *src, size_t n)
+{
+        char *d = dest;
+        const char *s = src;
+
+        if (d==s) return d;
+        if (s+n <= d || d+n <= s) return memcpy(d, s, n);
+
+        if (d<s) {
+                if ((uintptr_t)s % WS == (uintptr_t)d % WS) {
+                        while ((uintptr_t)d % WS) {
+                                if (!n--) return dest;
+                                *d++ = *s++;
+                        }
+                        for (; n>=WS; n-=WS, d+=WS, s+=WS) *(WT *)d = *(WT *)s;
+                }
+                for (; n; n--) *d++ = *s++;
+        } else {
+                if ((uintptr_t)s % WS == (uintptr_t)d % WS) {
+                        while ((uintptr_t)(d+n) % WS) {
+                                if (!n--) return dest;
+                                d[n] = s[n];
+                        }
+                        while (n>=WS) n-=WS, *(WT *)(d+n) = *(WT *)(s+n);
+                }
+                while (n) n--, d[n] = s[n];
+        }
+
+        return dest;
+}