Add support for DW_AT_data_location.

Add support for DW_AT_data_location.

gdb/ChangeLog:

        * gdbtypes.h (struct main_type): Add field "data_location".
        (TYPE_DATA_LOCATION, TYPE_DATA_LOCATION_BATON)
        (TYPE_DATA_LOCATION_ADDR, TYPE_DATA_LOCATION_KIND): New macros.
        * gdbtypes.c (is_dynamic_type): Return 1 if the type has
        a dynamic data location.
        (resolve_dynamic_type): Add DW_AT_data_location handling.
        (copy_recursive, copy_type): Copy the data_location information
        when present.
        * dwarf2read.c (set_die_type): Add DW_AT_data_location handling.
        * value.c (value_from_contents_and_address): Add
        DW_AT_data_location handling.