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.
