swift234

IRGen: Fix LLVM verifier failure with class casts when the source is an optional

We can't bitcast an i64 into an i8*, we have to do an int to pointer
cast instead.

This exposes a new issue, where dynamic casts do not support casting
from Optional<A> to A -- tracked in <rdar://problem/23122310>.

Fixes <rdar://problem/23055035>.

Swift SVN r32704