Put (void)val; here and there to tell gcc we used the variable.

The spin_lock wrappers do not use the return value of the functions they
wrap, resulting in dozens of compiler warnings because they are inline
functions. There is no elegant solution to this, I hope using (void)val;
is the least shocking alternative.

include/vlc_threads_funcs.h

@@ -581,6 +581,7 @@ static inline void vlc_spin_lock (vlc_spinlock_t *spin)
 {
     int val = pthread_spin_lock (&spin->spin);
     assert (val == 0);
+    (void)val;
 }
 
 /**
@@ -590,6 +591,7 @@ static inline void vlc_spin_unlock (vlc_spinlock_t *spin)
 {
     int val = pthread_spin_unlock (&spin->spin);
     assert (val == 0);
+    (void)val;
 }
 
 /**
@@ -599,6 +601,7 @@ static inline void vlc_spin_destroy (vlc_spinlock_t *spin)
 {
     int val = pthread_spin_destroy (&spin->spin);
     assert (val == 0);
+    (void)val;
 }
 
 #elif defined( WIN32 )