Greatly improve the speed if looking up DWARF line number information.

Greatly improve the speed if looking up DWARF line number information.

	* dwarf2.c (comp_unit): Add new fields 'lookup_funcinfo_table' and
	'number_of_functions' to keep lookup table and number of entries in
	the table.
	(line_sequence): Add new fields 'line_info_lookup' and 'num_lines'
	to keep lookup table and number of entries in the table.
	(lookup_funcinfo): New structure for lookup table for function
	references.
	(build_line_info_table): New function to create and build the lookup
	table for line information.
	(lookup_address_in_line_info_table): Use the lookup table instead of
	traverse a linked list.
	(compare_lookup_funcinfos): New compare fuction used in sorting of
	lookup table for function references.
	(build_lookup_funcinfo_table): New function to create, build and
	sort the lookup table for functions references.
	(lookup_address_in_function_table): Use the table instead of
	traverse a linked list.
	(_bfd_dwarf2_cleanup_debug_info): Free memory from function references
	lookup table.