Fixes to get PR #364 working on MSVC

c++/src/kj/thread.c++

@@ -42,7 +42,7 @@ Thread::~Thread() noexcept(false) {
   if (!detached) {
     KJ_ASSERT(WaitForSingleObject(threadHandle, INFINITE) != WAIT_FAILED);
 
-    KJ_IF_MAYBE(e, exception) {
+    KJ_IF_MAYBE(e, state->exception) {
       kj::throwRecoverableException(kj::mv(*e));
     }
   }
@@ -125,7 +125,7 @@ void* Thread::runThread(void* ptr) {
 
 void Thread::ThreadState::unref() {
 #if _MSC_VER
-  if (_InterlockedDecrement_rel(&refcount)) {
+  if (_InterlockedDecrement(&refcount)) {
     _ReadBarrier();
 #else
   if (__atomic_sub_fetch(&refcount, 1, __ATOMIC_RELEASE) == 0) {

c++/src/kj/thread.h

@@ -59,7 +59,7 @@ private:
     Function<void()> func;
     kj::Maybe<kj::Exception> exception;
 
-    int refcount;
+    unsigned int refcount;
     // Owned by the parent thread and the child thread.
 
     void unref();