tar: fix reproducibility issue

Force root/root as names for uid0/gid0 instead of using the system
names. This helps make packed download tarballs more reproducible

Signed-off-by: Felix Fietkau <nbd@nbd.name>

tools/tar/patches/100-symlink-force-root-name.patch

@@ -0,0 +1,22 @@
+Force root/root as names for uid0/gid0 instead of using the system
+names. This helps make packed download tarballs more reproducible
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+---
+--- a/src/create.c
++++ b/src/create.c
+@@ -545,12 +545,8 @@ write_gnu_long_link (struct tar_stat_inf
+   char *tmpname;
+ 
+   header = start_private_header ("././@LongLink", size, 0);
+-  uid_to_uname (0, &tmpname);
+-  UNAME_TO_CHARS (tmpname, header->header.uname);
+-  free (tmpname);
+-  gid_to_gname (0, &tmpname);
+-  GNAME_TO_CHARS (tmpname, header->header.gname);
+-  free (tmpname);
++  UNAME_TO_CHARS ("root", header->header.uname);
++  GNAME_TO_CHARS ("root", header->header.gname);
+ 
+   strcpy (header->buffer + offsetof (struct posix_header, magic),
+ 	  OLDGNU_MAGIC);