dotnet-build will produce a deps file for portable builds, and will now
create "runnable" outputs for RID-less targets
the outputs won't actually be runnable today because we need corehost
changes and to generate a deps.json file for corehost to use.
Update .exe's project.json Target Framework from dnxcore50 to netstandardapp1.5.
Update .dll's project.json Target Framework from dnxcore50 to netstandard1.3.
Adding workaround for DataContractSerialization to src\dotnet\project.json to fix crossgen issue.
Build 23901 has a dependency issue that doesn't allow the runtime.any.System.Private.DataContractSerialization
package to be restored. When we move to a new build of CoreFX we should take this workaround out.
