Restore GetTargetFrameworkProperties temporarily

This is a compat shim, and should be reverted once
dotnet/msbuild#1866 is available for use in the SDK. It will not be
used with common targets that contain that change.

Author: rainersigwald

src/Tasks/Microsoft.NET.Build.Tasks/build/Microsoft.NET.Sdk.Common.targets

@@ -103,5 +103,28 @@ Copyright (c) .NET Foundation. All rights reserved.
       </ProjectBuildInstructions>
     </ItemGroup>
   </Target>
-  
+
+  <!-- This target is a compat shim, allowing the SDK to continue to function with older common targets that haven't switched to GetReferenceProperties.
+
+       TODO: After the SDK has picked up an MSBuild with https://github.com/Microsoft/msbuild/pull/1866, it should be deleted. -->
+  <Target Name="GetTargetFrameworkProperties" Returns="TargetFramework=$(NearestTargetFramework);ProjectHasSingleTargetFramework=$(_HasSingleTargetFramework);ProjectIsRidAgnostic=$(_IsRidAgnostic)"
+          DependsOnTargets="ShouldQueryForProperties">
+
+    <PropertyGroup>
+      <!-- If a ReferringTargetFramework was not specified, and we only have one TargetFramework, then don't try to check compatibility -->
+      <_SkipNearestTargetFrameworkResolution Condition="'$(TargetFramework)' != '' and '$(ReferringTargetFramework)' == ''">true</_SkipNearestTargetFrameworkResolution>
+      <NearestTargetFramework Condition="'$(_SkipNearestTargetFrameworkResolution)' == 'true'">$(TargetFramework)</NearestTargetFramework>
+
+      <_PossibleTargetFrameworks Condition="'$(TargetFramework)' != ''">$(TargetFramework)</_PossibleTargetFrameworks>
+      <_PossibleTargetFrameworks Condition="'$(TargetFramework)' == ''">$(TargetFrameworks)</_PossibleTargetFrameworks>
+    </PropertyGroup>
+
+    <GetNearestTargetFramework ReferringTargetFramework="$(ReferringTargetFramework)"
+                               PossibleTargetFrameworks="$(_PossibleTargetFrameworks)"
+                               ProjectFilePath="$(MSBuildProjectFullPath)"
+                               Condition="'$(_SkipNearestTargetFrameworkResolution)' != 'true'">
+      <Output PropertyName="NearestTargetFramework" TaskParameter="NearestTargetFramework" />
+    </GetNearestTargetFramework>
+  </Target>
+
 </Project>