use [[gnu::...]] attributes

src/tag/Handler.hxx

@@ -5,7 +5,6 @@
 #define MPD_TAG_HANDLER_HXX
 
 #include "Chrono.hxx"
-#include "util/Compiler.h"
 
 #include <cstddef>
 #include <cstdint>

src/tag/Id3Scan.cxx

@@ -55,7 +55,7 @@
 #define ID3_FRAME_MOOD "TMOO"
 #endif
 
-gcc_pure
+[[gnu::pure]]
 static Id3String
 tag_id3_getstring(const struct id3_frame *frame, unsigned i) noexcept
 {
@@ -186,7 +186,7 @@ tag_id3_import_comment(const struct id3_tag *tag, const char *id, TagType type,
  * Parse a TXXX name, and convert it to a TagType enum value.
  * Returns TAG_NUM_OF_ITEM_TYPES if the TXXX name is not understood.
  */
-gcc_pure
+[[gnu::pure]]
 static TagType
 tag_id3_parse_txxx_name(const char *name) noexcept
 {

src/tag/ReplayGainParser.cxx

@@ -43,7 +43,7 @@ ParseReplayGainTag(ReplayGainInfo &info,
 		const char *name;
 		const char *value;
 
-		gcc_pure
+		[[gnu::pure]]
 		const char *operator[](const char *n) const noexcept {
 			return StringEqualsCaseASCII(name, n)
 				? value
@@ -60,7 +60,7 @@ ParseReplayGainVorbis(ReplayGainInfo &info, std::string_view entry) noexcept
 	struct VorbisCommentEntry {
 		std::string_view entry;
 
-		gcc_pure
+		[[gnu::pure]]
 		const char *operator[](std::string_view n) const noexcept {
 			return GetVorbisCommentValue(entry, n).data();
 		}