More fixes for memory access violations triggered by running readelf on fuzzed binaries.

More fixes for memory access violations triggered by running readelf on fuzzed binaries.

	PR binutils/17531
	* dwarf.c (read_and_display_attr_value): Test for a block length
	being so long that it wraps around to before the start of the block.
	(process_debug_info): Test for section_begin wrapping around to
	before the start of the section.
	(display_gdb_index): Test for num_cus being so large that the end
	address wraps around to before the start of the section.
	(process_cu_tu_index): Test for j being so large that the section
	index pool wraps around to before the start of the section.