HostQueue: Don't use dispatch_sync to run code synchronously

This method may choose to run on the current thread as an optimization.
Since we may try to call DOLHostQueueRunSync on the main thread, we don't want this.

Source/iOS/Library/HostQueue.mm

@@ -4,6 +4,10 @@
 #include "HostQueue.h"
 
 #include <dispatch/dispatch.h>
+#include <Foundation/Foundation.h>
+
+#include "Common/Assert.h"
+#include "Common/Event.h"
 
 #include "Core/Core.h"
 
@@ -21,6 +25,8 @@ dispatch_queue_t DOLHostQueueGetUnderlyingQueue()
 
 void DOLHostQueueExecuteBlock(void (^block)(void))
 {
+  ASSERT(![NSThread isMainThread]);
+
   Core::DeclareAsHostThread();
 
   block();
@@ -30,9 +36,16 @@ void DOLHostQueueExecuteBlock(void (^block)(void))
 
 void DOLHostQueueRunSync(void (^block)(void))
 {
-  dispatch_sync(DOLHostQueueGetUnderlyingQueue(), ^{
+  Common::Event sync_event;
+  Common::Event* sync_event_ptr = &sync_event;
+
+  dispatch_async(DOLHostQueueGetUnderlyingQueue(), ^{
     DOLHostQueueExecuteBlock(block);
+
+    sync_event_ptr->Set();
   });
+
+  sync_event.Wait();
 }
 
 void DOLHostQueueRunAsync(void (^block)(void))