Fix eventlog tests

Author: stephentoub

src/libraries/Directory.Build.targets

@@ -174,7 +174,8 @@
   </ItemGroup>
 
   <!-- Adds polyfills on non-.NETCoreApp builds -->
-  <ItemGroup Condition="'$(MSBuildProjectExtension)' == '.csproj' and
+  <ItemGroup Condition="'$(SkipIncludePolyfills)' != 'true' and
+                        '$(MSBuildProjectExtension)' == '.csproj' and
                         '$(IsTestProject)' != 'true' and
                         '$(IsTestSupportProject)' != 'true' and
                         '$(TargetFrameworkIdentifier)' != '.NETCoreApp'">

src/libraries/System.Diagnostics.EventLog/src/Messages/System.Diagnostics.EventLog.Messages.csproj

@@ -6,5 +6,7 @@
     <!-- Override the parent Directory.Build.props -->
     <SupportedOSPlatforms />
     <EnableLibraryImportGenerator>false</EnableLibraryImportGenerator>
+    <SkipIncludePolyfills>true</SkipIncludePolyfills>
+    <SkipIncludeNullableAttributes>true</SkipIncludeNullableAttributes>
   </PropertyGroup>
 </Project>