Fix a few more miscellaneous (harmless) Clang warnings.

headers/os/media/MediaDefs.h

@@ -18,7 +18,7 @@
 #endif
 
 
-struct media_node;
+class media_node;
 
 #define B_MEDIA_NAME_LENGTH 64
 

src/add-ons/kernel/file_systems/bfs/BPlusTree.h

@@ -361,7 +361,7 @@ private:
 private:
 			friend class TreeIterator;
 			friend class CachedNode;
-			friend class TreeCheck;
+			friend struct TreeCheck;
 
 			Inode*				fStream;
 			bplustree_header	fHeader;

src/add-ons/media/plugins/ffmpeg/AVCodecDecoder.cpp

@@ -81,10 +81,11 @@ struct avformat_codec_context {
 
 // profiling related globals
 #define DO_PROFILING 0
-
+#if DO_PROFILING
 static bigtime_t decodingTime = 0;
 static bigtime_t conversionTime = 0;
 static long profileCounter = 0;
+#endif
 
 
 AVCodecDecoder::AVCodecDecoder()