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

fusl/src/string/strchrnul.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 *__strchrnul(const char *s, int c)
+{
+        size_t *w, k;
+
+        c = (unsigned char)c;
+        if (!c) return (char *)s + strlen(s);
+
+        for (; (uintptr_t)s % ALIGN; s++)
+                if (!*s || *(unsigned char *)s == c) return (char *)s;
+        k = ONES * c;
+        for (w = (void *)s; !HASZERO(*w) && !HASZERO(*w^k); w++);
+        for (s = (void *)w; *s && *(unsigned char *)s != c; s++);
+        return (char *)s;
+}
+
+weak_alias(__strchrnul, strchrnul);