Convert gnu-v3-abi.c to new hash table

This converts gnu-v3-abi.c to use the new hash table.

This change shows how a std::vector can easily be made directly from
the hash table, simplifying the earlier approach of constructing a
vector and a hash table at the same time.

Change-Id: Ia0c387a035a52300db6b6f5a3a2e5c69efa01155
Co-Authored-By: Tom Tromey <tom@tromey.com>
Approved-By: Tom Tromey <tom@tromey.com>