[libc] Attempt to speed up memcpy for aligned mem

Copy long-by-long instead of byte-by-byte if both pointers are similarly
aligned.

src/libraries/libc/string/memcpy.c

@@ -10,9 +10,24 @@ void * memcpy( void * restrict s1, const void * restrict s2, size_t n )
 {
     char * dest = (char *) s1;
     const char * src = (const char *) s2;
-    while ( n-- )
+
-    {
+	if (((uintptr_t)src & 7) == ((uintptr_t)dest & 7)) {
+		while (((uintptr_t)src & 7) && n--)
+			*dest++ = *src++;
+
+		const uint64_t *srcq = (const uint64_t*)src;
+		uint64_t *destq = (uint64_t*)dest;
+		while (n >= 8) {
+			*destq++ = *srcq++;
+			n -= 8;
+		}
+
+		src = (const char*)srcq;
+		dest = (char*)destq;
+	}
+
+    while (n--)
         *dest++ = *src++;
-    }
+
     return s1;
 }