remove gcc_unused

[[maybe_unused]] (introduced in C++17) is standard C++.

https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
says that this is equivalent to the GNU unused attribute.

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

src/output/plugins/HaikuOutputPlugin.cxx

@@ -81,9 +81,9 @@ private:
 	std::chrono::steady_clock::duration Delay() const noexcept override;
 
 	static void _FillBuffer(void* cookie, void* _buffer, size_t size,
-		gcc_unused const media_raw_audio_format& _format);
+		[[maybe_unused]] const media_raw_audio_format& _format);
 	void FillBuffer(void* _buffer, size_t size,
-		gcc_unused const media_raw_audio_format& _format);
+		[[maybe_unused]] const media_raw_audio_format& _format);
 
 	void SendTag(const Tag &tag) override;
 };
@@ -154,7 +154,7 @@ HaikuOutput::_FillBuffer(void* cookie, void* buffer, size_t size,
 
 void
 HaikuOutput::FillBuffer(void* _buffer, size_t size,
-	gcc_unused const media_raw_audio_format& _format)
+	[[maybe_unused]] const media_raw_audio_format& _format)
 {
 
 	buffer = (uint8*)_buffer;

src/output/plugins/NullOutputPlugin.cxx

@@ -53,7 +53,7 @@ private:
 			: std::chrono::steady_clock::duration::zero();
 	}
 
-	size_t Play(gcc_unused const void *chunk, size_t size) override {
+	size_t Play([[maybe_unused]] const void *chunk, size_t size) override {
 		if (sync) {
 			if (!timer->IsStarted())
 				timer->Start();

src/output/plugins/OSXOutputPlugin.cxx

@@ -710,9 +710,9 @@ osx_output_set_device(OSXOutput *oo)
  */
 static OSStatus
 osx_render(void *vdata,
-	   gcc_unused AudioUnitRenderActionFlags *io_action_flags,
-	   gcc_unused const AudioTimeStamp *in_timestamp,
-	   gcc_unused UInt32 in_bus_number,
+	   [[maybe_unused]] AudioUnitRenderActionFlags *io_action_flags,
+	   [[maybe_unused]] const AudioTimeStamp *in_timestamp,
+	   [[maybe_unused]] UInt32 in_bus_number,
 	   UInt32 in_number_frames,
 	   AudioBufferList *buffer_list)
 {

src/output/plugins/PipeOutputPlugin.cxx

@@ -57,7 +57,7 @@ PipeOutput::PipeOutput(const ConfigBlock &block)
 }
 
 inline void
-PipeOutput::Open(gcc_unused AudioFormat &audio_format)
+PipeOutput::Open([[maybe_unused]] AudioFormat &audio_format)
 {
 	fh = popen(cmd.c_str(), "w");
 	if (fh == nullptr)

src/output/plugins/PulseOutputPlugin.cxx

@@ -62,7 +62,7 @@ class PulseOutput final : AudioOutput {
 public:
 	void SetMixer(PulseMixer &_mixer);
 
-	void ClearMixer(gcc_unused PulseMixer &old_mixer) {
+	void ClearMixer([[maybe_unused]] PulseMixer &old_mixer) {
 		assert(mixer == &old_mixer);
 
 		mixer = nullptr;
@@ -277,8 +277,8 @@ pulse_wait_for_operation(struct pa_threaded_mainloop *mainloop,
  * the caller thread, to wake pulse_wait_for_operation() up.
  */
 static void
-pulse_output_stream_success_cb(gcc_unused pa_stream *s,
-			       gcc_unused int success, void *userdata)
+pulse_output_stream_success_cb([[maybe_unused]] pa_stream *s,
+			       [[maybe_unused]] int success, void *userdata)
 {
 	PulseOutput &po = *(PulseOutput *)userdata;
 
@@ -342,7 +342,7 @@ PulseOutput::OnServerLayoutChanged(pa_subscription_event_type_t t,
 }
 
 static void
-pulse_output_subscribe_cb(gcc_unused pa_context *context,
+pulse_output_subscribe_cb([[maybe_unused]] pa_context *context,
 			  pa_subscription_event_type_t t,
 			  uint32_t idx, void *userdata)
 {
@@ -508,7 +508,7 @@ PulseOutput::WaitConnection()
 }
 
 inline void
-PulseOutput::OnStreamSuspended(gcc_unused pa_stream *_stream)
+PulseOutput::OnStreamSuspended([[maybe_unused]] pa_stream *_stream)
 {
 	assert(_stream == stream || stream == nullptr);
 	assert(mainloop != nullptr);
@@ -574,7 +574,7 @@ PulseOutput::OnStreamWrite(size_t nbytes)
 }
 
 static void
-pulse_output_stream_write_cb(gcc_unused pa_stream *stream, size_t nbytes,
+pulse_output_stream_write_cb([[maybe_unused]] pa_stream *stream, size_t nbytes,
 			     void *userdata)
 {
 	PulseOutput &po = *(PulseOutput *)userdata;

src/output/plugins/httpd/HttpdOutputPlugin.cxx

@@ -121,7 +121,7 @@ HttpdOutput::OnDeferredBroadcast() noexcept
 
 void
 HttpdOutput::OnAccept(UniqueSocketDescriptor fd,
-		      SocketAddress, gcc_unused int uid) noexcept
+		      SocketAddress, [[maybe_unused]] int uid) noexcept
 {
 	/* the listener socket has become readable - a client has
 	   connected */

src/output/plugins/sles/SlesOutputPlugin.cxx

@@ -111,7 +111,7 @@ private:
 	 * been consumed.  It synthesises and enqueues the next
 	 * buffer.
 	 */
-	static void PlayedCallback(gcc_unused SLAndroidSimpleBufferQueueItf caller,
+	static void PlayedCallback([[maybe_unused]] SLAndroidSimpleBufferQueueItf caller,
 				   void *pContext)
 	{
 		SlesOutput &sles = *(SlesOutput *)pContext;