Fix missing System.Text.Encoding.Codepages on OSX
Fix missing System.Text.Encoding.Codepages on OSX

cdmihai/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,mono/msbuild,rainersigwald/msbuild,chipitsine/msbuild,AndyGerlicher/msbuild,chipitsine/msbuild,jeffkl/msbuild,sean-gilliam/msbuild,mono/msbuild,rainersigwald/msbuild,rainersigwald/msbuild,jeffkl/msbuild,sean-gilliam/msbuild,AndyGerlicher/msbuild,jeffkl/msbuild,cdmihai/msbuild,cdmihai/msbuild,Microsoft/msbuild,cdmihai/msbuild,mono/msbuild,Microsoft/msbuild,Microsoft/msbuild,chipitsine/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,jeffkl/msbuild,Microsoft/msbuild,mono/msbuild,chipitsine/msbuild