elf: Never set non_ir_ref_regular for debug reference

Never set non_ir_ref_regular for debug reference since references in
debug sections shouldn't impact LTO output.

	* elflink.c (elf_link_add_object_symbols): Don't check strip for
	references in debug sections when setting non_ir_ref_regular.

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