Work around spurious MSVC noexcept dtor compile error

c++/src/kj/common.h

@@ -794,6 +794,15 @@ class Maybe;
 
 namespace _ {  // private
 
+#if _MSC_VER
+  // TODO(msvc): MSVC barfs on noexcept(instance<T&>().~T()) where T = kj::Exception and
+  // kj::_::Void. It and every other factorization I've tried produces:
+  //   error C2325: 'kj::Blah' unexpected type to the right of '.~': expected 'void'
+#define MSVC_NOEXCEPT_DTOR_WORKAROUND(T) __is_nothrow_destructible(T)
+#else
+#define MSVC_NOEXCEPT_DTOR_WORKAROUND(T) noexcept(instance<T&>().~T())
+#endif
+
 template <typename T>
 class NullableValue {
   // Class whose interface behaves much like T*, but actually contains an instance of T and a
@@ -818,7 +827,7 @@ public:
       ctor(value, other.value);
     }
   }
-  inline ~NullableValue() noexcept(noexcept(instance<T&>().~T())) {
+  inline ~NullableValue() noexcept(MSVC_NOEXCEPT_DTOR_WORKAROUND(T)) {
     if (isSet) {
       dtor(value);
     }