Consistency check for merge sections

Consistency check for merge sections

We can't allow sections to be merged and sized by the ELF linker
backend and then later be output by the generic linker backend.  The
generic linker backend doesn't understand merge sections.

	PR ld/19013
	* elflink.c (_bfd_elf_merge_sections): Only merge input bfds that
	will be handled by elf_link_input_bfd.  Rename abfd param to obfd.