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

fusl/src/string/strtok_r.c

Index: fusl/src/string/strtok_r.c
diff --git a/fusl/src/string/strtok_r.c b/fusl/src/string/strtok_r.c
new file mode 100644
index 0000000000000000000000000000000000000000..862d4fe48550fdb7f3c97f2f271f98fb34206dd0
--- /dev/null
+++ b/fusl/src/string/strtok_r.c
@@ -0,0 +1,12 @@
+#include <string.h>
+
+char *strtok_r(char *restrict s, const char *restrict sep, char **restrict p)
+{
+	if (!s && !(s = *p)) return NULL;
+	s += strspn(s, sep);
+	if (!*s) return *p = 0;
+	*p = s + strcspn(s, sep);
+	if (**p) *(*p)++ = 0;
+	else *p = 0;
+	return s;
+}