x86: Use hehdr_start for __ehdr_start

Use hehdr_start for __ehdr_start instead of elf_link_hash_lookup.

	* elfxx-x86.c (elf_x86_linker_defined): Use hehdr_start if name
	is NULL.
	(_bfd_x86_elf_link_check_relocs): Pass NULL as __ehdr_start to
	elf_x86_linker_defined.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>