swift234

SIL Serialization: handle more SILInstructins.

Handle the following SILInstructions:
LoadWeakInst,
Checked Conversion instructions:
  DowncastInst, SuperToArchetypeRefInst,
  DowncastArchetypeAddrInst, DowncastArchetypeRefInst,
  ProjectDowncastExistentialAddrInst, DowncastExistentialRefInst

Add an optional 2-bit field for instruction attributes to SILOneOperandLayout
and SILOneTypeOneOperandLayout.

Update SILPrinter to print [take] for LoadWeakInst.


Swift SVN r8416