Use InterlockedExchangeAdd varient instead of InterlockedAdd which doesn't seem to be available on …

runtime/vm/atomic_win.h

Index: runtime/vm/atomic_win.h
diff --git a/runtime/vm/atomic_win.h b/runtime/vm/atomic_win.h
index 410c1a2bf1986a7e7d5a3c11f485607266501ff2..2ade768e2f19e33f86afc840fb2b239500a4a82f 100644
--- a/runtime/vm/atomic_win.h
+++ b/runtime/vm/atomic_win.h
@@ -32,12 +32,12 @@ inline uintptr_t AtomicOperations::FetchAndIncrementBy(intptr_t* p,
                                                        intptr_t value) {
 #if defined(HOST_ARCH_X64)
   return static_cast<uintptr_t>(
-      InterlockedAdd64(reinterpret_cast<LONGLONG*>(p),
-                       static_cast<LONGLONG>(value))) - value;
+      InterlockedExchangeAdd64(reinterpret_cast<LONGLONG*>(p),
+                               static_cast<LONGLONG>(value)));
 #elif defined(HOST_ARCH_IA32)
   return static_cast<uintptr_t>(
-      InterlockedAdd(reinterpret_cast<LONG*>(p),
-                     static_cast<LONG>(value))) - value;
+      InterlockedExchangeAdd(reinterpret_cast<LONG*>(p),
+                             static_cast<LONG>(value)));
 #else
 #error Unsupported host architecture.
 #endif
@@ -61,12 +61,12 @@ inline uintptr_t AtomicOperations::FetchAndDecrementBy(intptr_t* p,
                                                        intptr_t value) {
 #if defined(HOST_ARCH_X64)
   return static_cast<uintptr_t>(
-      InterlockedAdd64(reinterpret_cast<LONGLONG*>(p),
-                       static_cast<LONGLONG>(-value))) + value;
+      InterlockedExchangeAdd64(reinterpret_cast<LONGLONG*>(p),
+                               static_cast<LONGLONG>(-value)));
 #elif defined(HOST_ARCH_IA32)
   return static_cast<uintptr_t>(
-      InterlockedAdd(reinterpret_cast<LONG*>(p),
-                     static_cast<LONG>(-value))) + value;
+      InterlockedExchangeAdd(reinterpret_cast<LONG*>(p),
+                             static_cast<LONG>(-value)));
 #else
 #error Unsupported host architecture.
 #endif