swift234

Expose the ModuleFile in SerializedASTFile so that the underlying Module (and thus SILModule) can be retrieved when deserializing.

This is necessary since if one wishes to write a secondary tool with swift
headers, one can not access the ModuleFile in SerializedASTFile since to do so
would require you to be a friend of the class, something that would create a
build dependency in between the secondary tool and the swift libraries.

Swift SVN r14171