swift234

SIL Serialization: add handling of types.

For PolymorphicFunctionType used in a SILFunction, we don't have a
corresponding Decl to share the parameter list with. In that case,
we set the owning Decl ID to 0 and add a trailing param lists.

We add a helper function to find the TypeAliasDecl for a Builtin type.
If the lookup is expensive, we can cache the lookup.

Deserializing SILBasicBlock and SILInstruction is not implemented yet.

SIL serializer and deserializer are implicitly tested when a module
contains transparant SILFunctions.


Swift SVN r8230