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.