added primitive semaphore

semaphore.h

@@ -0,0 +1,12 @@
+/*
+ * Copyright 2022 Oleg Borodin  <borodin@unix7.org>
+ */
+
+
+typedef struct {
+    int value;
+} sem_t;
+
+int sem_init(sem_t* sem, int value);
+int sem_wait(sem_t* sem);
+int sem_post(sem_t* sem);