Attempt to fix MacOS build

include/vlc_threads_funcs.h

@@ -507,7 +507,7 @@ static inline int __vlc_cond_wait( const char * psz_file, int i_line,
     /* In debug mode, timeout */
     struct timespec timeout;
 
-# if (_POSIX_CLOCK_MONOTONIC - 0 >= 0)
+# if defined (_POSIX_CLOCK_MONOTONIC) && (_POSIX_CLOCK_MONOTONIC >= 0)
     if( clock_gettime( CLOCK_MONOTONIC, &timeout ) )
 # endif
         clock_gettime( CLOCK_REALTIME, &timeout );

src/misc/threads.c

@@ -464,7 +464,7 @@ int __vlc_cond_init( vlc_object_t *p_this, vlc_cond_t *p_condvar )
     if (ret)
         return ret;
 
-# if defined (HAVE_CLOCK_NANOSLEEP) && (_POSIX_CLOCK_MONOTONIC - 0 >= 0)
+# if defined (_POSIX_CLOCK_MONOTONIC) && (_POSIX_CLOCK_MONOTONIC >= 0)
     /* This must be the same clock as the one in mtime.c */
     pthread_condattr_setclock (&attr, CLOCK_MONOTONIC);
 # endif