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

fusl/include/semaphore.h

+#ifndef _SEMAPHORE_H
+#define _SEMAPHORE_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <features.h>
+
+#define __NEED_time_t
+#define __NEED_struct_timespec
+#include <bits/alltypes.h>
+
+#include <fcntl.h>
+
+#define SEM_FAILED ((sem_t *)0)
+
+typedef struct {
+        volatile int __val[4*sizeof(long)/sizeof(int)];
+} sem_t;
+
+int    sem_close(sem_t *);
+int    sem_destroy(sem_t *);
+int    sem_getvalue(sem_t *__restrict, int *__restrict);
+int    sem_init(sem_t *, int, unsigned);
+sem_t *sem_open(const char *, int, ...);
+int    sem_post(sem_t *);
+int    sem_timedwait(sem_t *__restrict, const struct timespec *__restrict);
+int    sem_trywait(sem_t *);
+int    sem_unlink(const char *);
+int    sem_wait(sem_t *);
+
+#ifdef __cplusplus
+}
+#endif
+#endif