redox: Add semaphore functions

(backport <#5051>)
(cherry picked from commit 30fd290)

Author: willnode

libc-test/semver/redox.txt

@@ -337,6 +337,14 @@ qsort
 reallocarray
 renameat2
 rlim_t
+sem_clockwait
+sem_destroy
+sem_getvalue
+sem_init
+sem_post
+sem_timedwait
+sem_trywait
+sem_wait
 setgrent
 setpwent
 setresgid

src/unix/redox/mod.rs

@@ -1309,6 +1309,17 @@ extern "C" {
         result: *mut *mut passwd,
     ) -> c_int;
 
+    // semaphore.h
+    pub fn sem_destroy(sem: *mut sem_t) -> c_int;
+    pub fn sem_init(sem: *mut sem_t, pshared: c_int, value: c_uint) -> c_int;
+    pub fn sem_clockwait(
+        sem: *mut sem_t,
+        clock_id: clockid_t,
+        abstime: *const crate::timespec,
+    ) -> c_int;
+    pub fn sem_timedwait(sem: *mut sem_t, abstime: *const crate::timespec) -> c_int;
+    pub fn sem_getvalue(sem: *mut sem_t, sval: *mut c_int) -> c_int;
+
     // signal.h
     pub fn pthread_sigmask(
         how: c_int,