Some build fixes when cross compiling

Author: azeno

src/ImmutableObjectGraph.Generation/ImmutableObjectGraph.Generation.csproj

@@ -4,6 +4,7 @@
     <TargetFramework>netstandard2.0</TargetFramework>
     <Description>MSBuild-based code generator to transform simple mutable type definitions into fully functional immutable types with persistent characteristics.</Description>
 
+    <EnforceExtendedAnalyzerRules>true</EnforceExtendedAnalyzerRules>
     <IncludeBuildOutput>false</IncludeBuildOutput>
     <GetTargetPathDependsOn>$(GetTargetPathDependsOn);GetDependencyTargetPaths</GetTargetPathDependsOn>
     <TargetsForTfmSpecificContentInPackage>$(TargetsForTfmSpecificContentInPackage);PackBuildOutputs</TargetsForTfmSpecificContentInPackage>

src/NuGet.Config

@@ -5,7 +5,7 @@
   </config>
   <packageSources>
     <clear />
-    <add key="api.nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
     <add key="myget.org/F/aarnott" value="https://www.myget.org/F/aarnott/api/v3/index.json" protocolVersion="3" />
   </packageSources>
 </configuration>