osdep/semaphore_osx.c: Include osdep/semaphore.h before #ifdef

osdep/semaphore.h is the file that defines the very #define that is
tested in the #ifdef that wraps its inclusion, so it was never compiled.

osdep/semaphore_osx.c

@@ -11,6 +11,8 @@
  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
+#include "osdep/semaphore.h"
+
 #ifdef MP_SEMAPHORE_EMULATION
 
 #include <unistd.h>
@@ -21,9 +23,6 @@
 
 #include "osdep/io.h"
 
-#include "semaphore.h"
-
-
 int mp_sem_init(mp_sem_t *sem, int pshared, unsigned int value)
 {
     if (pshared) {