* elfcpp_file.h: Fix header guard. Include <cstdio>.
(class Elf_recognizer): New class, code from gold/object.cc.
(Elf_file::find_section_by_type): New method.
gold/:
* incremental.cc: Include <cstdarg> and "target-select.h".
(vexplain_no_incremental): New function.
(explain_no_incremental): New function.
(Incremental_binary::error): New method.
(Sized_incremental_binary::do_find_incremental_inputs_section): New
method.
(make_sized_incremental_binary): New function.
(open_incremental_binary): New function.
(can_incrementally_link_file): Add checks if output is ELF and has
inputs section.
* incremental.h: Include "elfcpp_file.h" and "output.h".
(Incremental_binary): New class.
(Sized_incremental_binary): New class.
(open_incremental_binary): Declare.
* object.cc (is_elf_object): Use
elfcpp::Elf_recognizer::is_elf_file.
(make_elf_object): Use elfcpp::Elf_recognizer::is_valid_header.
* output.h (Output_file::filesize): New method.
(Elf_file::large_shndx_offset): New function.
(Elf_file::construct): Initialize large_shndx_offset_.
(Elf_File::initialize_shnum): If necessary, adjust shstrndx_ and
set large_shndx_offset_.
