Revert r175626, "ADT/Optional.h: Appease msvc."

Sorry, I didn't cover +Asserts, by accident. :(

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175633 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/ADT/Optional.h

@@ -70,7 +70,7 @@ public:
 
   void reset() {
     if (hasVal) {
-      (**this).~T();
+      (*this)->~T();
       hasVal = false;
     }
   }