Replace an existing flag for cross-references to member types (that
wasn't getting much use) with one consistent with how we lookup
values. This fixes the case where someone actually has a useful type
as a member of a protocol extension, and that type gets referenced in
another module; Dispatch does exactly this.
Because you can currently only define typealiases in protocol
extensions, not new types, there's always a workaround for someone
hitting this issue: just use the underlying type.
https://bugs.swift.org/browse/SR-4076
In most cases this means adding @public to things that get serialized;
in a few cases it means using a modern public stdlib API instead of
a legacy thing I was trying to keep @internal.
Swift SVN r19350
...but don't do anything with them yet. This does check that they're being
correctly serialized, though.
This introduces a new ADT, PointerIntUnion, which like PointerUnion is an
efficient variant type using the lowest bit of data as a discriminator.
By default, the union can store any pointer-bits-minus-one-sized integer,
but both the integer type and the underlying storage type can be
customized.
Swift SVN r5321
