* dwarf_reader.cc (next_generation_count): New static var.

	* dwarf_reader.cc (next_generation_count): New static var.
	(Addr2line_cache_entry): New struct.
	(addr2line_cache): New static var.
	(Dwarf_line_info::one_addr2line): Added caching.
	(Dwarf_line_info::clear_addr2line_cache): New function.
	* dwarf_reader.h (Dwarf_line_info::one_addr2line): Add
	cache-size parameter.
	(Dwarf_line_info::one_addr2line_cache): New function.
	* symtab.cc (Symbol_table::detect_odr_violations): Pass
	new cache-size argument to one_addr2line(), and clear cache.