Change dwarf2_initialize_objfile's return value

Change dwarf2_initialize_objfile's return value

dwarf2_initialize_objfile was returning boolean whether it is psymtabs
or .gdb_index while now it needs to return also whether it is
.debug_names.

gdb/ChangeLog
2017-12-08  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* defs.h (elf_sym_fns_lazy_psyms, elf_sym_fns_gdb_index): Move here
	declarations from elfread.c.
	(dwarf2_initialize_objfile): Change return value.
	* elfread.c (elf_sym_fns_lazy_psyms, elf_sym_fns_gdb_index): Move these
	declarations to defs.h.
	(elf_symfile_read): Adjust dwarf2_initialize_objfile caller.
	* symfile.h (dwarf2_initialize_objfile): Change return type.