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

fusl/src/string/strchrnul.c

Index: fusl/src/string/strchrnul.c
diff --git a/fusl/src/string/strchrnul.c b/fusl/src/string/strchrnul.c
new file mode 100644
index 0000000000000000000000000000000000000000..05700ad64eea55cb8f6dffad0fe6dd97feb3d31c
--- /dev/null
+++ b/fusl/src/string/strchrnul.c
@@ -0,0 +1,26 @@
+#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);