tar: port to --without-xattrs --enable-gcc-warnings

Reported by Pavel Raiskup in
<http://lists.gnu.org/archive/html/bug-tar/2013-03/msg00029.html>.
* src/xattrs.c (xattrs__fd_set) [!HAVE_XATTRS]: Omit.

src/xattrs.c

@@ -484,6 +484,7 @@ xattrs_xattrs_get (int parentfd, char const *file_name,
     }
 }
 
+#ifdef HAVE_XATTRS
 static void
 xattrs__fd_set (struct tar_stat_info const *st,
                 char const *file_name, char typeflag,
@@ -509,6 +510,7 @@ xattrs__fd_set (struct tar_stat_info const *st,
 		  sysname, attr, file_name));
     }
 }
+#endif
 
 /* lgetfileconat is called against FILE_NAME iff the FD parameter is set to
    zero, otherwise the fgetfileconat is used against correct file descriptor */