LibPthread: Set errno in sem_trywait()

Author: https://github.com/TSultanov
Commit: 15cce56411
Pull-request: https://github.com/SerenityOS/serenity/pull/14260
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibPthread/semaphore.cpp

@@ -93,15 +93,19 @@ int sem_trywait(sem_t* sem)
 {
     u32 value = AK::atomic_load(&sem->value, AK::memory_order_relaxed);
     u32 count = value & ~POST_WAKES;
-    if (count == 0)
-        return EAGAIN;
+    if (count == 0) {
+        errno = EAGAIN;
+        return -1;
+    }
     // Decrement the count without touching the flag.
     u32 desired = (count - 1) | (value & POST_WAKES);
     bool exchanged = AK::atomic_compare_exchange_strong(&sem->value, value, desired, AK::memory_order_acquire);
-    if (exchanged) [[likely]]
+    if (exchanged) [[likely]] {
         return 0;
-    else
-        return EAGAIN;
+    } else {
+        errno = EAGAIN;
+        return -1;
+    }
 }
 
 // https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_wait.html