*: use gcc.h macros instead of GLib

src/pcm/PcmBuffer.cxx

@@ -24,7 +24,7 @@
 /**
  * Align the specified size to the next 8k boundary.
  */
-G_GNUC_CONST
+constexpr
 static size_t
 align_8k(size_t size)
 {

src/pcm/PcmDsdUsb.cxx

@@ -22,14 +22,14 @@
 #include "PcmBuffer.hxx"
 #include "AudioFormat.hxx"
 
-G_GNUC_CONST
+constexpr
 static inline uint32_t
 pcm_two_dsd_to_usb_marker1(uint8_t a, uint8_t b)
 {
 	return 0xff050000 | (a << 8) | b;
 }
 
-G_GNUC_CONST
+constexpr
 static inline uint32_t
 pcm_two_dsd_to_usb_marker2(uint8_t a, uint8_t b)
 {

src/pcm/PcmResampleInternal.hxx

@@ -65,7 +65,7 @@ pcm_resample_lsr_32(PcmResampler *state,
 		    unsigned channels,
 		    unsigned src_rate,
 		    const int32_t *src_buffer,
-		    G_GNUC_UNUSED size_t src_size,
+		    size_t src_size,
 		    unsigned dest_rate, size_t *dest_size_r,
 		    GError **error_r);
 
@@ -84,7 +84,7 @@ pcm_resample_fallback_32(PcmResampler *state,
 			 unsigned channels,
 			 unsigned src_rate,
 			 const int32_t *src_buffer,
-			 G_GNUC_UNUSED size_t src_size,
+			 size_t src_size,
 			 unsigned dest_rate,
 			 size_t *dest_size_r);
 

src/pcm/PcmVolume.cxx

@@ -64,7 +64,7 @@ pcm_volume_change_16(int16_t *buffer, const int16_t *end, int volume)
  * multiplication result instead of emulating 64 bit multiplication.
  */
 static inline int32_t
-pcm_volume_sample_24(int32_t sample, int32_t volume, G_GNUC_UNUSED int32_t dither)
+pcm_volume_sample_24(int32_t sample, int32_t volume, gcc_unused int32_t dither)
 {
 	int32_t result;