The code used "isa" to check the type and then "getAs" to look through
sugar; we need to look through the sugar when checking, too, otherwise
any kind of sugar (nullability qualifiers in the example; or a
typedef) will thwart this semantic check. Fixes rdar://problem/23804250.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@255066 91177308-0d34-0410-b5e6-96231b3b80d8