dwarf_loader: Fix sorting of Rust structs

We may have structs with fields on the same offset, don't move anything
in that case, otherwise we get into an eternal loop, doh.

Tested with the Linux kernel built with CONFIG_RUST + all the code
examples, first Rust struct where this happened was:

  (gdb) p type->namespace.name
  $2 = 0x7fffda938497 "((), char)"
  (gdb) p type->nr_members
  $3 = 2
  (gdb) p current_member->name
  $4 = 0x7fffda918f36 "__1"
  (gdb) p next_member->name
  $5 = 0x7fffda91765c "__0"
  (gdb) p current_member->byte_offset
  $6 = 0
  (gdb) p next_member->byte_offset
  $7 = 0

But this shows that --lang_exclude should be better positioned as we're
now needlessly loading all the tags for Rust DWARF to then just trow it
away at the cu__filter() in pahole :-\

Too late in the 1.25 release cycle for that, optimize it in 1.26.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

dwarf_loader.c

@@ -2857,7 +2857,7 @@ static int type__sort_by_offset(struct tag *tag, struct cu *cu, void *cookie __m
 
 		struct class_member *next_member = list_entry(current_member->tag.node.next, typeof(*current_member), tag.node);
 
-		if (current_member->byte_offset < next_member->byte_offset)
+		if (current_member->byte_offset <= next_member->byte_offset)
 			continue;
 
 		list_del(&current_member->tag.node);