*: use gcc.h macros instead of GLib

src/decoder/DsdiffDecoderPlugin.cxx

@@ -477,8 +477,8 @@ dsdiff_stream_decode(struct decoder *decoder, struct input_stream *is)
 
 static bool
 dsdiff_scan_stream(struct input_stream *is,
-		   G_GNUC_UNUSED const struct tag_handler *handler,
-		   G_GNUC_UNUSED void *handler_ctx)
+		   gcc_unused const struct tag_handler *handler,
+		   gcc_unused void *handler_ctx)
 {
 	DsdiffMetaData metadata;
 	DsdiffChunkHeader chunk_header;

src/decoder/DsfDecoderPlugin.cxx

@@ -309,8 +309,8 @@ dsf_stream_decode(struct decoder *decoder, struct input_stream *is)
 
 static bool
 dsf_scan_stream(struct input_stream *is,
-		   G_GNUC_UNUSED const struct tag_handler *handler,
-		   G_GNUC_UNUSED void *handler_ctx)
+		gcc_unused const struct tag_handler *handler,
+		gcc_unused void *handler_ctx)
 {
 	/* check DSF metadata */
 	DsfMetaData metadata;

src/decoder/FfmpegDecoderPlugin.cxx

@@ -73,7 +73,7 @@ level_ffmpeg_to_glib(int level)
 }
 
 static void
-mpd_ffmpeg_log_callback(G_GNUC_UNUSED void *ptr, int level,
+mpd_ffmpeg_log_callback(gcc_unused void *ptr, int level,
 			const char *fmt, va_list vl)
 {
 	const AVClass * cls = NULL;
@@ -185,7 +185,7 @@ ffmpeg_find_audio_stream(const AVFormatContext *format_context)
 	return -1;
 }
 
-G_GNUC_CONST
+gcc_const
 static double
 time_from_ffmpeg(int64_t t, const AVRational time_base)
 {
@@ -195,7 +195,7 @@ time_from_ffmpeg(int64_t t, const AVRational time_base)
 		/ (double)1024;
 }
 
-G_GNUC_CONST
+gcc_const
 static int64_t
 time_to_ffmpeg(double t, const AVRational time_base)
 {
@@ -301,7 +301,7 @@ ffmpeg_send_packet(struct decoder *decoder, struct input_stream *is,
 	return cmd;
 }
 
-G_GNUC_CONST
+gcc_const
 static SampleFormat
 ffmpeg_sample_format(enum AVSampleFormat sample_fmt)
 {

src/decoder/FlacDecoderPlugin.cxx

@@ -56,7 +56,7 @@ static void flacPrintErroredState(FLAC__StreamDecoderState state)
 	g_warning("%s\n", FLAC__StreamDecoderStateString[state]);
 }
 
-static void flacMetadata(G_GNUC_UNUSED const FLAC__StreamDecoder * dec,
+static void flacMetadata(gcc_unused const FLAC__StreamDecoder * dec,
 			 const FLAC__StreamMetadata * block, void *vdata)
 {
 	flac_metadata_common_cb(block, (struct flac_data *) vdata);

src/decoder/FluidsynthDecoderPlugin.cxx

@@ -64,7 +64,7 @@ fluidsynth_level_to_glib(enum fluid_log_level level)
  * logging library.
  */
 static void
-fluidsynth_mpd_log_function(int level, char *message, G_GNUC_UNUSED void *data)
+fluidsynth_mpd_log_function(int level, char *message, gcc_unused void *data)
 {
 	g_log(G_LOG_DOMAIN, fluidsynth_level_to_glib(fluid_log_level(level)),
 	      "%s", message);
@@ -199,8 +199,8 @@ fluidsynth_file_decode(struct decoder *decoder, const char *path_fs)
 
 static bool
 fluidsynth_scan_file(const char *file,
-		     G_GNUC_UNUSED const struct tag_handler *handler,
-		     G_GNUC_UNUSED void *handler_ctx)
+		     gcc_unused const struct tag_handler *handler,
+		     gcc_unused void *handler_ctx)
 {
 	return fluid_is_midifile(file);
 }

src/decoder/SndfileDecoderPlugin.cxx

@@ -67,9 +67,9 @@ sndfile_vio_read(void *ptr, sf_count_t count, void *user_data)
 }
 
 static sf_count_t
-sndfile_vio_write(G_GNUC_UNUSED const void *ptr,
-		  G_GNUC_UNUSED sf_count_t count,
-		  G_GNUC_UNUSED void *user_data)
+sndfile_vio_write(gcc_unused const void *ptr,
+		  gcc_unused sf_count_t count,
+		  gcc_unused void *user_data)
 {
 	/* no writing! */
 	return -1;

src/decoder/VorbisDecoderPlugin.cxx

@@ -87,7 +87,7 @@ static int ogg_seek_cb(void *data, ogg_int64_t offset, int whence)
 }
 
 /* TODO: check Ogg libraries API and see if we can just not have this func */
-static int ogg_close_cb(G_GNUC_UNUSED void *data)
+static int ogg_close_cb(gcc_unused void *data)
 {
 	return 0;
 }

src/decoder/WavpackDecoderPlugin.cxx

@@ -92,7 +92,7 @@ format_samples_int(int bytes_per_sample, void *buffer, uint32_t count)
  * This function converts floating point sample data to 24-bit integer.
  */
 static void
-format_samples_float(G_GNUC_UNUSED int bytes_per_sample, void *buffer,
+format_samples_float(gcc_unused int bytes_per_sample, void *buffer,
 		     uint32_t count)
 {
 	float *p = (float *)buffer;