Pass $(Nullable) to csc. (#6093)
Pass $(Nullable) to csc. (#6093)

$(Nullable) not passed into csc invoked in XamlPreCompile, caused nullable warnings in projects with xaml and nullable enabled.
mono/msbuild,rainersigwald/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,mono/msbuild,mono/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,mono/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,sean-gilliam/msbuild,AndyGerlicher/msbuild,AndyGerlicher/msbuild,rainersigwald/msbuild