Memory region allocated by alloca() carries no implicit type information.
Don't crash when resolving the init message for an Objective-C object
that is being constructed in such region.

rdar://problem/32517077

Differential Revision: https://reviews.llvm.org/D33828


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@305211 91177308-0d34-0410-b5e6-96231b3b80d8