Update signing.targets to disable full signing on unix

Issue dotnet/roslyn#8210 blocks signing
on unix, but we still need to have the assemblies have the correct
identity so we are simply turning on DelaySigning for those assemblies.

Tools-Override/sign.targets

@@ -8,26 +8,29 @@
 
   <UsingTask AssemblyFile="$(BuildToolsTaskDir)Microsoft.DotNet.Build.Tasks.dll" TaskName="OpenSourceSign" />
   <UsingTask AssemblyFile="$(BuildToolsTaskDir)Microsoft.DotNet.Build.Tasks.dll" TaskName="WriteSigningRequired" />
-  
+
   <PropertyGroup Condition="'$(SkipSigning)'!='true'">
-    <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile Condition="'$(AssemblyOriginatorKeyFile)' == ''">$(ToolsDir)MSFT.snk</AssemblyOriginatorKeyFile>
     <AssemblyOriginatorKeyFile Condition="'$(UseECMAKey)' == 'true'">$(ToolsDir)ECMA.snk</AssemblyOriginatorKeyFile>
     <AssemblyOriginatorKeyFile Condition="'$(UseOpenKey)' == 'true'">$(ToolsDir)Open.snk</AssemblyOriginatorKeyFile>
 
     <!-- Don't sign test assemblies with the Microsoft Key, as this affects APIs checking if the test assembly is an MS Key -->
     <AssemblyOriginatorKeyFile Condition="'$(IsTestProject)' == 'true'">$(ToolsDir)Test.snk</AssemblyOriginatorKeyFile>
 
+    <SignAssembly>true</SignAssembly>
     <DelaySign>true</DelaySign>
-    <DelaySign Condition="'$(UseOpenKey)' == 'true'">false</DelaySign>
+
+    <!-- For full keys we should disable delay signing -->
+    <FullPublicPrivateKey Condition="'$(AssemblyOriginatorKeyFile)' == '$(ToolsDir)Open.snk'">true</FullPublicPrivateKey>
+    <FullPublicPrivateKey Condition="'$(AssemblyOriginatorKeyFile)' == '$(ToolsDir)Test.snk'">true</FullPublicPrivateKey>
+
+    <DelaySign Condition="'$(FullPublicPrivateKey)' == 'true'">false</DelaySign>
+
     <!--
-      We enable the signing for the test projects only on Windows because Roslyn not supporting full signing on non-Windows platforms.
-      Issue: https://github.com/dotnet/roslyn/issues/8210
+      Setting DelaySign to true when running build on unix because of Roslyn doesn't support full signing on non-windows.
+      See issue https://github.com/dotnet/roslyn/issues/8210.
     -->
-    <DelaySign Condition="'$(OSEnvironment)' == 'Windows_NT' And '$(IsTestProject)' == 'true'">false</DelaySign>
-
-    <SignType Condition="'$(SignType)'=='' And '$(UseOpenKey)' == 'true'">real</SignType>
-    <SignType Condition="'$(SignType)'=='' And '$(IsTestProject)' == 'true'">real</SignType>
+    <DelaySign Condition="'$(RunningOnUnix)' == 'true'">true</DelaySign>
 
     <DefineConstants>$(DefineConstants);SIGNED</DefineConstants>
     <!-- applicable values for SignType are oss, test or real -->
@@ -40,7 +43,7 @@
   <!-- writes a signing marker file containing the required signatures -->
   <Target Name="WriteSigningRequired"
           AfterTargets="AfterBuild"
-          Condition="'$(SkipSigning)' != 'true' and '$(IsTestProject)' != 'true' and '$(SignType)' != 'oss'"
+          Condition="'$(SkipSigning)' != 'true' and '$(FullPublicPrivateKey)' != 'true' and '$(SignType)' != 'oss'"
           Inputs="$(TargetPath)"
           Outputs="$(TargetPath).requires_signing">
     <WriteSigningRequired AuthenticodeSig="$(AuthenticodeSig)"