...fulfilling the promised audit from 0747d9a339. No intended
functionality change /other/ than the order of already-unsorted lists.
This affected a number of SIL tests that relied on deserialization
order matching the original source order; I have no idea why the old
hash logic would make that the case. If we think that's a valuable
property, we should serialize a list of functions in addition to the
iterable table. (Maybe just in SIB mode?)
This is technically a source break, but the @_fixed_layout attribute
is not official yet. If anyone really cares, we can make this
conditional on -swift-version 5 later, but I'd rather not.
This change is necessary so that we can give property initializers
non-public linkage. Currently they are public, because they can be
referenced from inlinable initializers.
Now that property initializers inside a @_fixed_layout type can
only reference public symbols, they no longer have to be public,
but making that change requires a bit more work.
