linker bfd.h tidy

linker bfd.h tidy

bfd/
	* bfd-in.h (bfd_symbol, bfd_section_already_linked),
	(bfd_elf_version_tree): Delete forward declarations.
	Move other forward decls and remaining elf function decl later.
	(bfd_section_already_linked_table_init),
	(bfd_section_already_linked_table_free),
	(_bfd_handle_already_linked, _bfd_nearby_section),
	(_bfd_fix_excluded_sec_syms): Move to bfdlink.h.
include/
	* bfdlink.h (struct bfd_section_already_linked): Forward declare.
	(bfd_section_already_linked_table_init),
	(bfd_section_already_linked_table_free),
	(_bfd_handle_already_linked, _bfd_nearby_section),
	(_bfd_fix_excluded_sec_syms): Declare.