use PACKED macro insted of open-coding GCC-ism

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/util-linux/volume_id/sysv.c b/util-linux/volume_id/sysv.c
index 7a99cd6..0e65072 100644
--- a/util-linux/volume_id/sysv.c
+++ b/util-linux/volume_id/sysv.c
@@ -48,7 +48,7 @@
 	uint32_t	s_state;
 	uint32_t	s_magic;
 	uint32_t	s_type;
-} __attribute__((__packed__));
+} PACKED;
 
 #define XENIX_NICINOD				100
 #define XENIX_NICFREE				100
@@ -74,7 +74,7 @@
 	uint8_t		s_fill[371];
 	uint32_t	s_magic;
 	uint32_t	s_type;
-} __attribute__((__packed__));
+} PACKED;
 
 #define SYSV_SUPERBLOCK_BLOCK			0x01
 #define SYSV_MAGIC				0xfd187e20