buildDotnetModule: generate a NuGet.config with source

Some references, like <Sdk />, ignore the --source argument.
To fix that, we generate a simple NuGet.config containing only
the given nuget source.

pkgs/build-support/dotnet/build-dotnet-module/hooks/dotnet-configure-hook.sh

@@ -26,6 +26,18 @@ dotnetConfigureHook() {
 
     (( "${#projectFile[@]}" == 0 )) && dotnetRestore
 
+    # Generate a NuGet.config file to make sure everything,
+    # including things like <Sdk /> dependencies, is restored from the proper source
+cat <<EOF > "./NuGet.config"
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="nugetSource" value="@nugetSource@/lib" />
+  </packageSources>
+</configuration>
+EOF
+
     for project in ${projectFile[@]} ${testProjectFile[@]-}; do
         dotnetRestore "$project"
     done