The DisassemblerLLVMC has a retain cycle - the InstructionLLVMC's contained in its instruction
list have a shared pointer back to their DisassemblerLLVMC.  This checkin force clears the InstructionList
in all the places we use the DisassemblerSP to stop the leaking for now.  I'll go back and fix this
for real when I have time to do so.

<rdar://problem/14581918>