See https://github.com/dotnet/source-build/issues/286
diff -ruN dotnet/targets/corefx.targets dotnet/targets/corefx.targets
--- dotnet/targets/corefx.targets 2017-10-25 20:40:18.000000000 -0400
+++ dotnet/targets/corefx.targets 2017-11-10 12:39:18.045215772 -0500
@@ -16,7 +16,7 @@
BeforeTargets="Package">
-
+
WorkingDirectory="$(ProjectDirectory)"
EnvironmentVariables="@(EnvironmentVariables)" />
</Target>