swift234

Replace "Members" arrays with an intrusive linked list.

The use of ASTContext-allocated arrays to store the members of nominal
type declarations and the extensions thereof is an
abomination. Instead, introduce the notion of an "iterable"
declaration context, which keeps track of the declarations within that
context (stored as a singly-linked list) and allows iteration over
them. When a member is added, it will also make sure that the member
goes into the lookup table for its context immediately.

This eliminates a ton of wasted memory when we have to reallocate the
members arrays for types and extensions, and moves us toward a much
more sane model. The only functionality change here is that the Clang
importer no longer puts subscript declarations into the wrong class,
nor does it nested a C struct within another C struct.



Swift SVN r16572