dwarf2out.c (hash_external_ref): Use die_symbol or signature for hash so that hash table traversal order is...

2013-06-10  Cary Coutant  <ccoutant@google.com>

gcc/
	* dwarf2out.c (hash_external_ref): Use die_symbol or signature
	for hash so that hash table traversal order is deterministic.

From-SVN: r199927