abg-elf-helpers: move some versioning helpers from abg-dwarf-reader

abg-elf-helpers: move some versioning helpers from abg-dwarf-reader

Move some definitions from abg-dwarf-reader to abg-elf-helpers that are
strictly only related to ELF.

	* abg-dwarf-reader.cc (get_symbol_versionning_sections): Move function out.
	(get_version_definition_for_versym): Likewise.
	(get_version_needed_for_versym): Likewise.
	(get_version_for_symbol): Likewise.
	* abg-elf-helpers.cc (get_symbol_versionning_sections): Move function in.
	(get_version_definition_for_versym): Likewise.
	(get_version_needed_for_versym): Likewise.
	(get_version_for_symbol): Likewise.
	* abg-elf-helpers.h (get_symbol_versionning_sections): Add declaration.
	(get_version_definition_for_versym): Likewise.
	(get_version_needed_for_versym): Likewise.
	(get_version_for_symbol): Likewise.

Reviewed-by: Giuliano Procida <gprocida@google.com>
Signed-off-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Dodji Seketeli <dodji@redhat.com>