* flags.h: Add flag_eliminate_unused_debug_types.
        * toplev.c: Add flag_eliminate_unused_debug_types.
        (f_options): Add -feliminate-unused-debug-types.
        * dwarf2out.c (struct file_table): Add emitted member.
        (splice_child_die): Fix the parent pointer for the child being
        spliced.
        (lookup_filename): Maintain file_table.emitted array.  Don't
        output .file directive here.
        (maybe_emit_file): (new)
        (init_file_table): Set up file_table.emitted.
        (dwarf2out_source_line): Use maybe_emit_file.
        (dwarf2out_start_source_file): Use maybe_emit_file.
        (dwarf2out_init): Use maybe_emit_file.
        (prune_unused_types_walk_attribs): (new)
        (prune_unused_types_mark): (new)
        (prune_unused_types_walk): (new)
        (prune_unused_types_prune): (new)
        (prune_unused_types): (new)
        (dwarf2out_finish): Call prune_unused_types if
        flag_eliminate_unused_debug_types is set.
        * doc/invoke.texi (Option Summary): Add
        -feliminate-unused-debug-types.
        (Debugging Options): Likewise.

From-SVN: r63588