* elf.c (elf_obj_tdata): Merge elf_obj_tdata_struct and

* elf.c (elf_obj_tdata):  Merge elf_obj_tdata_struct and
elf_core_tdata_struct into a single common struct.  Core files
wouldn't have worked at all without this.
(bfd_elf_find_section):  New function for GDB's undercover use
to find string sections that BFD hides from it.
(elf_get_str_section):  Avoid multiple alloc&reads for same data; lint.
(elf_object_p, elf_core_file_p):  Allocate internal file header
storage dynamically.
* bfd.c (union {...} tdata):  Remove elf_core_tdata_struct.
* demo64.c:  Prevent "empty translation unit" warnings from idiots.