Fix warnings trivial warnings.

Fix warnings about:
 . Unused variables
 . format mismatch in printf/scanf format string and arguments
 . Missing parenthesis around assignment as truth values
 . Clang warnings anout unknown GCC pragma

commands/mt/mt.c

@@ -199,7 +199,7 @@ SCSI tape drive %s:\n\
 				(long) mtget.mt_fileno,
 				(long) mtget.mt_blkno,
 				(long) mtget.mt_resid);
-			printf(mtget.mt_blksize == 0 ? "variable\n" : "%ld\n",
+			printf(mtget.mt_blksize == 0 ? "variable\n" : "%d\n",
 				mtget.mt_blksize);
 		}
 	}