[VM] Fix crash in x64-JIT: Disable  exactness tracking for fields with FutureOr<> type

Closes https://github.com/dart-lang/sdk/issues/34238

Change-Id: I0cb00737b3d3aad5fa6ea6359272bd43f89dbad9
Reviewed-on: https://dart-review.googlesource.com/71244
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
diff --git a/runtime/vm/class_finalizer.cc b/runtime/vm/class_finalizer.cc
index c52f150..a8e852a 100644
--- a/runtime/vm/class_finalizer.cc
+++ b/runtime/vm/class_finalizer.cc
@@ -1589,7 +1589,7 @@
   if (type.IsType() && !type.IsFunctionType() && !type.IsDartFunctionType() &&
       type.IsInstantiated()) {
     const Class& cls = Class::Handle(type.type_class());
-    return cls.IsGeneric();
+    return cls.IsGeneric() && !cls.IsFutureOrClass();
   }
 
   return false;