[analyzer] Re-enable reasoning about CK_LValueBitCast

It’s important for us to reason about the cast as it is used in std::addressof. The reason we did not
handle the cast previously was a crash on a test case (see commit r157478). The crash was in
processing array to pointer decay when the region type was not an array. Address the issue, by
just returning an unknown in that case.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@182808 91177308-0d34-0410-b5e6-96231b3b80d8