Second try at adding a compatibility symbol for the MemoryBase constructor.

Third-party libraries are currently trying to use the
MemoryBase constructor but failing because we fixed the
definition of ssize_t. This is a stop-gap for users of
this private API until we can get them fixed.

Bug: 8253769
Change-Id: Ie7c86f45fa39cb53539cab0ffe8585a585656714