Hopefully fix multithreading on MacOS

src/libFLAC/stream_encoder.c

@@ -45,8 +45,18 @@
 #endif
 #ifdef HAVE_PTHREAD
 #include <pthread.h>
+#ifdef __APPLE__
+/* Mac does have sem_init, but it doesn't work */
+#include <dispatch/dispatch.h>
+typedef dispatch_semaphore_t sem_t;
+#define sem_init(sem,x,val) ((*sem = dispatch_semaphore_create(val)) == NULL)
+#define sem_post(sem) dispatch_semaphore_signal(*sem)
+#define sem_wait(sem) dispatch_semaphore_wait(*sem, DISPATCH_TIME_FOREVER)
+#define sem_destroy(sem) dispatch_release(*sem)
+#else
 #include <semaphore.h>
 #endif
+#endif
 #include "share/compat.h"
 #include "FLAC/assert.h"
 #include "FLAC/stream_decoder.h"