package/binutils: xtensa: fix shrink_dynamic_reloc_sections

This fixes the following build error caused by link-time relaxation
removing copies of literals that reference undefined weak symbols with
PLT entries created due to -rdynamic option passed to g++ link command:

  ld: BFD (GNU Binutils) 2.31.1 internal error, aborting at
  elf32-xtensa.c:3292 in elf_xtensa_finish_dynamic_sections

Fixes:
http://autobuild.buildroot.net/results/d41/d41aae8a448c316187f9fbde40f1d077182bb244/


Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>