Fix warnings on clang

src/Album.h

@@ -53,7 +53,7 @@ class Album : public IAlbum, public Cache<Album, IAlbum, policy::AlbumTable>
         std::string m_id3tag;
 
         friend class Cache<Album, IAlbum, policy::AlbumTable>;
-        friend class policy::AlbumTable;
+        friend struct policy::AlbumTable;
 };
 
 #endif // ALBUM_H

src/AlbumTrack.h

@@ -50,7 +50,7 @@ class AlbumTrack : public IAlbumTrack, public Cache<AlbumTrack, IAlbumTrack, pol
         std::shared_ptr<Album> m_album;
 
         friend class Cache<AlbumTrack, IAlbumTrack, policy::AlbumTrackTable>;
-        friend class policy::AlbumTrackTable;
+        friend struct policy::AlbumTrackTable;
 };
 
 #endif // ALBUMTRACK_H

src/File.h

@@ -74,7 +74,7 @@ class File : public IFile, public Cache<File, IFile, policy::FileTable, policy::
         std::shared_ptr<ShowEpisode> m_showEpisode;
 
         friend class Cache<File, IFile, policy::FileTable, policy::FileCache>;
-        friend class policy::FileTable;
+        friend struct policy::FileTable;
 };
 
 #endif // FILE_H

src/Label.h

@@ -49,7 +49,7 @@ class Label : public ILabel, public Cache<Label, ILabel, policy::LabelTable, pol
         std::string m_name;
 
         friend class Cache<Label, ILabel, policy::LabelTable>;
-        friend class policy::LabelTable;
+        friend struct policy::LabelTable;
 };
 
 #endif // LABEL_H

src/Show.h

@@ -44,7 +44,7 @@ class Show : public IShow, public Cache<Show, IShow, policy::ShowTable>
         std::string m_tvdbId;
 
         friend class Cache<Show, IShow, policy::ShowTable>;
-        friend class policy::ShowTable;
+        friend struct policy::ShowTable;
 };
 
 #endif // SHOW_H

src/ShowEpisode.h

@@ -50,7 +50,7 @@ class ShowEpisode : public IShowEpisode, public Cache<ShowEpisode, IShowEpisode,
         std::shared_ptr<Show> m_show;
 
         friend class Cache<ShowEpisode, IShowEpisode, policy::ShowEpisodeTable>;
-        friend class policy::ShowEpisodeTable;
+        friend struct policy::ShowEpisodeTable;
 };
 
 #endif // SHOWEPISODE_H