[PATCH gold/21066] Consider C++ exception handling metadata during ICF

[Cary Coutant]

> +  typedef std::multimap<Section_id, Extra_identity_info> Extra_identity_list;
>
> Should use Unordered_multimap.

Oops, never mind this comment -- I didn't note the use of
multimap::equal_range(), so of course it needs to be a sorted
multimap.

-cary