PR 22843: ld, gold: Add --dependency-file option.

PR 22843: ld, gold: Add --dependency-file option.

gold/
	* options.h (class General_options): Add --dependency-file option.
	* fileread.cc (File_read::files_read): New static variable.
	(File_read::open): Add the file to the files_read list.
	(File_read::record_file_read): New static member function.
	(File_read::write_dependency_file): New static member function.
	* fileread.h (class File_read): Declare them.
	* layout.cc (Layout::read_layout_from_file): Call record_file_read.
	(Close_task_runner::run): Call write_dependency_file if
	--dependency-file was passed.

ld/
	* NEWS: Note --dependency-file.
	* ld.texi (Options): Document --dependency-file.
	* ldlex.h (enum option_values): Add OPTION_DEPENDENCY_FILE.
	* ld.h (ld_config_type): New member dependency_file.
	* lexsup.c (ld_options, parse_args): Parse --dependency-file.
	* ldmain.c (struct dependency_file): New type.
	(dependency_files, dependency_files_tail): New static variables.
	(track_dependency_files): New function.
	(write_dependency_file): New function.
	(main): Call it when --dependency-file was passed.
	* ldfile.c (ldfile_try_open_bfd): Call track_dependency_files.
	(ldfile_open_command_file_1): Likewise.
	* ldelf.c (ldelf_try_needed): Likewise.
	* pe-dll.c (pe_implied_import_dll): Likewise.