nbd: delete superfluous test for __GNUC__

Since <linux/compiler.h> already tests for __GNUC__, there's no point in nbd.h
repeating that test.
Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Cc: Paul Clements <paul.clements@steeleye.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/nbd.h

@@ -88,11 +88,7 @@ struct nbd_request {
 	char handle[8];
 	__be64 from;
 	__be32 len;
-}
-#ifdef __GNUC__
-	__attribute__ ((packed))
-#endif
-;
+} __attribute__ ((packed));
 
 /*
  * This is the reply packet that nbd-server sends back to the client after