Objective-C. Warn when @encode'ing provides an incomplete
type encoding because in certain cases, such as for vector
types, because we still haven't designed encoding for them.
rdar://9255564


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@216301 91177308-0d34-0410-b5e6-96231b3b80d8