swift234

[deserialization] Create the SILLoader for a SILModule lazily the first time deserialization occurs instead of when the SILModule is created.

This enables us to get around timing issues when we create a SILModule before we
have finished loading all Swift Modules.

This manifested itself in sil-opt where we were unable to deserialize from the
standard library when optimizing a separate *.sil file.

Swift SVN r15670