Report bfd_merge_sections error

	PR 32260
bfd/
	* elfxx-target.h (bfd_elfNN_bfd_merge_sections): Default to
	bfd_generic_merge_sections when using the generic linker.
	* elflink.c (_bfd_elf_merge_sections): Return error from
	_bfd_merge_sections.  Abort on wrong hash table.
ld/
	* ldlang.c (lang_process): Report bfd_merge_sections error.