* dwarf2out.c: Revert most of 2000-11-25 and 2001-01-24 changes.
        (LN_PROLOG_AS_LABEL, LN_PROLOG_END_LABEL): New.
        (size_of_line_prolog): Remove.
        (output_line_info): Compute prologue size via label difference.
        (lookup_filename): Return "unspecified" for <internal> and <built-in>.

        * configure.in (HAVE_AS_DWARF2_DEBUG_LINE): Require that the
        assembler error when redefining file numbers.
        * config.in, configure: Rebuild.

From-SVN: r40559