swift234

SILGen: Steal stupid cleanup support from IRGen
Port over the basic machinery to push and pop cleanups from IRGen, and implement simple straight-line cleanup emission. Add a basic cleanup for VarDecls as a proof of concept. More sophisticated handling of outflows, dormant/alive/dead states, etc. still needs to be carried over. Breaks test/SIL/statements.swift due to lack of support for cleanups through branches.

Swift SVN r3196