[clang-tidy] use override instead of virtual

Found with modernize-use-override

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/output/plugins/AlsaOutputPlugin.cxx

@@ -210,7 +210,7 @@ class AlsaOutput final
 public:
 	AlsaOutput(EventLoop &loop, const ConfigBlock &block);
 
-	~AlsaOutput() noexcept {
+	~AlsaOutput() noexcept override {
 		/* free libasound's config cache */
 		snd_config_update_free_global();
 	}

src/output/plugins/AoOutputPlugin.cxx

@@ -53,7 +53,7 @@ class AoOutput final : AudioOutput, SafeSingleton<AoInit> {
 	size_t frame_size;
 
 	AoOutput(const ConfigBlock &block);
-	~AoOutput();
+	~AoOutput() override;
 
 public:
 	static AudioOutput *Create(EventLoop &, const ConfigBlock &block) {

src/output/plugins/FifoOutputPlugin.cxx

@@ -44,7 +44,7 @@ class FifoOutput final : AudioOutput {
 public:
 	FifoOutput(const ConfigBlock &block);
 
-	~FifoOutput() {
+	~FifoOutput() override {
 		CloseFifo();
 	}
 

src/output/plugins/ShoutOutputPlugin.cxx

@@ -49,7 +49,7 @@ struct ShoutOutput final : AudioOutput {
 	uint8_t buffer[32768];
 
 	explicit ShoutOutput(const ConfigBlock &block);
-	~ShoutOutput();
+	~ShoutOutput() override;
 
 	static AudioOutput *Create(EventLoop &event_loop,
 				   const ConfigBlock &block);