Revert Decl's iterators back to pointer value_type rather than reference value_type

In addition, I've made the pointer and reference typedef 'void' rather than T*
just so they can't get misused. I would've omitted them entirely but
std::distance likes them to be there even if it doesn't use them.

This rolls back r155808 and r155869.

Review by Doug Gregor incorporating feedback from Chandler Carruth.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158104 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 0f95747..19ac616 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -2835,7 +2835,7 @@
     return;
   }
 
-  FieldDecl *FirstField = &*Field;
+  FieldDecl *FirstField = *Field;
   QualType FirstType = FirstField->getType();
   if (FirstType->hasFloatingRepresentation() || FirstType->isVectorType()) {
     S.Diag(FirstField->getLocation(),