Enable feature runtime-async

Author: BCSharp

Directory.Build.props

@@ -143,4 +143,10 @@
     <CheckForOverflowUnderflow>false</CheckForOverflowUnderflow>
     <DefineConstants>$(PythonSymbols);$(Features);$(SignedSym);DEBUG;TRACE</DefineConstants>
   </PropertyGroup>
+
+  <!-- Runtime-async opt-in. Done AFTER DefineConstants is computed so the compiler-feature name
+       (which contains '=' and '-') does not leak into C# preprocessor symbols.-->
+  <PropertyGroup Condition="$(Features.Contains('FEATURE_RUNTIME_ASYNC'))">
+    <Features>$(Features);runtime-async=on</Features>
+  </PropertyGroup>
 </Project>

eng/net11.0.props

@@ -23,11 +23,13 @@
     <Features>$(Features);FEATURE_METADATA_READER</Features>
     <Features>$(Features);FEATURE_MMAP</Features>
     <Features>$(Features);FEATURE_NATIVE</Features>
+    <Features>$(Features);FEATURE_NET_ASYNC</Features>
     <Features>$(Features);FEATURE_OSPLATFORMATTRIBUTE</Features>
     <Features>$(Features);FEATURE_PIPES</Features>
     <Features>$(Features);FEATURE_PROCESS</Features>
     <Features>$(Features);FEATURE_REFEMIT</Features>
     <Features>$(Features);FEATURE_REGISTRY</Features>
+    <Features>$(Features);FEATURE_RUNTIME_ASYNC</Features>
     <Features>$(Features);FEATURE_RUNTIMEINFORMATION</Features>
     <Features>$(Features);FEATURE_SECURITY_RULES</Features>
     <Features>$(Features);FEATURE_STACK_TRACE</Features>