Improve the DWARF decoder's ability to describe the DW_AT_discr_list attribute.

Improve the DWARF decoder's ability to describe the DW_AT_discr_list attribute.

	PR 24510
	* dwarf.c (MAX_CU_NESTING): New constant.
	(level_type_signed): New static array.
	(skip_attr_bytes): New function.
	(get_type_signedness): New function.
	(read_and_print_leb128): New function.
	(display_discr_list): New function.
	(read_and_display_attr_value): Add start parameter.
	Use new functions when handling DW_AT_type and DW_AT_discr_list.
	(read_and_display_attr): Add start parameter.  Pass to
	read_and_display_attr_value.
	(process_debug_info): Update call to read_and_display_attr.
	(display_formatted_table): Likewise.
	(display_debug_lines_decoded): Likewise.  Also add start
	parameter.
	(display_debug_lines): Likewise.
	* testsuite/binutils-all/dwarf-attributes.S: Update discrimination
	lists.
	* testsuite/binutils-all/dwarf-attributes.W: Update expected
	output.