Fix crash in codegen on casting to `bool &`.

Currently codegen crashes trying to emit casting to bool &. It happens because bool type is converted to i1 and later then lvalue for reference is converted to i1*. But when codegen tries to load this lvalue it crashes trying to load value from this i1*.

Differential Revision: http://reviews.llvm.org/D13325

llvm-svn: 249534