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/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp b/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
index 7e5720d..757a4ce 100644
--- a/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/LLVMConventionsChecker.cpp
@@ -231,7 +231,7 @@
   for (RecordDecl::field_iterator I = R->field_begin(), E = R->field_end();
        I != E; ++I) {
     ASTFieldVisitor walker(R, BR);
-    walker.Visit(&*I);
+    walker.Visit(*I);
   }
 }
 
@@ -247,7 +247,7 @@
     const RecordDecl *RD = RT->getDecl()->getDefinition();
     for (RecordDecl::field_iterator I = RD->field_begin(), E = RD->field_end();
          I != E; ++I)
-      Visit(&*I);
+      Visit(*I);
   }
 
   FieldChain.pop_back();