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

fusl/include/threads.h

+#ifndef _THREADS_H
+#define _THREADS_H
+
+#include <features.h>
+#include <time.h>
+
+#ifdef __cplusplus
+extern "C" {
+typedef unsigned long thrd_t;
+#else
+typedef struct __pthread *thrd_t;
+#define thread_local _Thread_local
+#endif
+
+typedef int once_flag;
+typedef unsigned tss_t;
+typedef int (*thrd_start_t)(void *);
+typedef void (*tss_dtor_t)(void *);
+
+#define __NEED_cnd_t
+#define __NEED_mtx_t
+
+#include <bits/alltypes.h>
+
+#define TSS_DTOR_ITERATIONS 4
+
+enum {
+        thrd_success  = 0,
+        thrd_busy     = 1,
+        thrd_error    = 2,
+        thrd_nomem    = 3,
+        thrd_timedout = 4,
+};
+
+enum {
+        mtx_plain     = 0,
+        mtx_recursive = 1,
+        mtx_timed     = 2,
+};
+
+#define ONCE_FLAG_INIT 0
+
+int thrd_create(thrd_t *, thrd_start_t, void *);
+_Noreturn void thrd_exit(int);
+
+int thrd_detach(thrd_t);
+int thrd_join(thrd_t, int *);
+
+int thrd_sleep(const struct timespec *, struct timespec *);
+void thrd_yield(void);
+
+thrd_t thrd_current(void);
+int thrd_equal(thrd_t, thrd_t);
+#ifndef __cplusplus
+#define thrd_equal(A, B) ((A) == (B))
+#endif
+
+void call_once(once_flag *, void (*)(void));
+
+int mtx_init(mtx_t *, int);
+void mtx_destroy(mtx_t *);
+
+int mtx_lock(mtx_t *);
+int mtx_timedlock(mtx_t *__restrict, const struct timespec *__restrict);
+int mtx_trylock(mtx_t *);
+int mtx_unlock(mtx_t *);
+
+int cnd_init(cnd_t *);
+void cnd_destroy(cnd_t *);
+
+int cnd_broadcast(cnd_t *);
+int cnd_signal(cnd_t *);
+
+int cnd_timedwait(cnd_t *__restrict, mtx_t *__restrict, const struct timespec *__restrict);
+int cnd_wait(cnd_t *, mtx_t *);
+
+int tss_create(tss_t *, tss_dtor_t);
+void tss_delete(tss_t key);
+
+int tss_set(tss_t, void *);
+void *tss_get(tss_t);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif