Improve ODR checking in gold.

Improve ODR checking in gold.

gold/
	* debug.h (DEBUG_LOCATION): New.
	(DEBUG_ALL): Include DEBUG_LOCATION.
	(debug_string_to_enum): Add DEBUG_LOCATION.
	* dwarf_reader.cc (Sized_dwarf_line_info::read_lines): Fix debug
	output to print correct context.
	(Sized_dwarf_line_info::do_addr2line): Add debug output. Return
	up to 4 more locations at the beginning of the function.
	* symtab.cc (Symbol_table::detect_odr_violations): Get canonical
	result before sorting list of line numbers.
	* testsuite/debug_msg.sh: Allow range of line numbers for
	canonical results on optimized code.