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.