Add support for tracing of IRELATIVE PLT entries

- Because the IRELATIVE entries have no associated symbol name, we
  need to allow arch_elf_add_plt_entry to override the name.  This is
  done by that callback returning PLT_OK and returning the new symbol
  via libsym-chain return argument.  Filtering is postponed until we
  have that symbol, and the filter is applied to the whole returned
  chain.

- Add linux_elf_add_plt_entry_irelative to support proper naming of
  IRELATIVE PLT entries.  This needs to be called from arch backend,
  as the numbers of IRELATIVE relocations differ per-architecture.
3 files changed