std::vector::iterator type may be a pointer, then
iterator::value_type fails to compile since iterator is not a class,
namespace, or enumeration.
Patch by orivej (Orivej Desh)
Differential Revision: https://reviews.llvm.org/D52142
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@342354 91177308-0d34-0410-b5e6-96231b3b80d8