xtensa: fix relaxation of undefined weak references in shared objects

xtensa: fix relaxation of undefined weak references in shared objects

The change c451bb34ae8b ("xtensa: don't emit dynamic relocation for weak
undefined symbol") didn't properly handle shrinking of relocation
sections due to coalescing of references to a dynamic undefined weak
symbol in a shared object, which resulted in the following assertion
failure in ld when linking uClibc-ng libthread_db for xtensa:

  BFD (GNU Binutils) 2.31 internal error, aborting at elf32-xtensa.c:3269
  in elf_xtensa_finish_dynamic_sections

Shrink dynamic relocations section for dynamic undefined weak symbols
when linking a shared object.

bfd/
2018-07-23  Max Filippov  <jcmvbkbc@gmail.com>

	* elf32-xtensa.c (shrink_dynamic_reloc_sections): Shrink dynamic
	relocations section for dynamic undefined weak symbols when
	linking a shared object.