swift234

SILGen: Fix memory leak when sub-expression of ErasureExpr throws

If we didn't initialize the existential, we have to emit a cleanup
because we may have allocated a buffer on the heap to store the value.

Factor out the TakeExistentialCleanup that appears in a few places,
rename it to DeinitExistentialCleanup and add support for deallocating
boxed existentials.

Then, use a special Initialization subclass to keep track of the
state of the memory in emit{AddressOnly,Boxed}Erasure().

Swift SVN r31259