Merge branch 'IxAsyncCSharp8' of https://github.com/dotnet/reactive into IxAsyncCSharp8

Ix.NET/Source/Directory.build.targets

@@ -14,11 +14,6 @@
     <DefineConstants>$(DefineConstants);USE_ASYNC_ITERATOR</DefineConstants>
   </PropertyGroup>
   <PropertyGroup Condition="'$(TargetFramework)' == 'netcoreapp3.0' or '$(TargetFramework)' == 'netstandard2.1'">
-    <!--
-    NB: USE_ASYNC_ITERATOR relies on members in the framework only present in .NET Core 3.0 Preview 2 at the moment:
-          error CS0518: Predefined type 'System.Runtime.CompilerServices.AsyncIteratorMethodBuilder' is not defined or imported
-          error CS0656: Missing compiler required member 'System.Threading.Tasks.Sources.ManualResetValueTaskSourceCore`1.*
-    -->
     <DefineConstants>$(DefineConstants);USE_ASYNC_ITERATOR;HAS_ASYNCENUMERABLE;HAS_ASYNCDISPOSABLE;BCL_HAS_CONFIGUREAWAIT</DefineConstants>
   </PropertyGroup>
 
@@ -26,6 +21,11 @@
     <Product>$(AssemblyName) ($(TargetFramework))</Product>
   </PropertyGroup>
   
+  <ItemGroup>
+    <!-- Workaround https://github.com/dotnet/sdk/issues/2976 -->
+    <PackageReference Update="Microsoft.NETCore.Platforms" PrivateAssets="All" />
+  </ItemGroup>
+  
   <PropertyGroup Condition="'$(IsTestProject)' == 'true'">
     <UseSourceLink>true</UseSourceLink>
     <CoverletOutputFormat>cobertura</CoverletOutputFormat>

azure-pipelines.ix.yml

@@ -1,4 +1,4 @@
-trigger:
+ntrigger:
   branches:
     include:
       - master
@@ -22,7 +22,7 @@ pr:
       - azure-pipelines.ix.yml
 
 pool:
-  vmImage: vs2017-win2016
+  vmImage: windows-2019
 
 variables: 
   BuildConfiguration: Release