[ADT] Try again to use the same version of llvm::Optional on all compilers

The miscompile doesn't reproduce for me anymore with GCC 7.3. I'll watch
the buildbots closely.

Having different versions of Optional is an ABI violation when linking
GCC- and clang-built code together.

llvm-svn: 342637

llvm/include/llvm/ADT/Optional.h

@@ -108,7 +108,6 @@ template <typename T, bool IsPodLike> struct OptionalStorage {
   }
 };
 
-#if !defined(__GNUC__) || defined(__clang__) // GCC up to GCC7 miscompiles this.
 /// Storage for trivially copyable types only.
 template <typename T> struct OptionalStorage<T, true> {
   AlignedCharArrayUnion<T> storage;
@@ -125,7 +124,6 @@ template <typename T> struct OptionalStorage<T, true> {
 
   void reset() { hasVal = false; }
 };
-#endif
 } // namespace optional_detail
 
 template <typename T> class Optional {