build: ignore Windows projects in Mac sln configs

Author: mjcheetham

Git-Credential-Manager.sln

@@ -199,13 +199,9 @@ Global
 		{8DBBAB0A-970D-4BE3-958C-8CDC92F76549}.WindowsRelease|Any CPU.ActiveCfg = Release|Any CPU
 		{8DBBAB0A-970D-4BE3-958C-8CDC92F76549}.WindowsRelease|Any CPU.Build.0 = Release|Any CPU
 		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.MacDebug|Any CPU.ActiveCfg = Debug|Any CPU
-		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.MacDebug|Any CPU.Build.0 = Debug|Any CPU
 		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.MacRelease|Any CPU.ActiveCfg = Release|Any CPU
-		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.MacRelease|Any CPU.Build.0 = Release|Any CPU
 		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.Release|Any CPU.Build.0 = Release|Any CPU
 		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.WindowsDebug|Any CPU.ActiveCfg = Debug|Any CPU
 		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.WindowsDebug|Any CPU.Build.0 = Debug|Any CPU
 		{4C2DBC8A-B3F2-4C64-870A-BA79DA4BD403}.WindowsRelease|Any CPU.ActiveCfg = Release|Any CPU

src/windows/GitHub.UI.Windows/GitHub.UI.Windows.csproj

@@ -13,6 +13,10 @@
     <ProjectReference Include="..\..\shared\Microsoft.Git.CredentialManager\Microsoft.Git.CredentialManager.csproj" />
   </ItemGroup>
 
+  <ItemGroup Condition="'$(OSPlatform)' != 'windows'">
+    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0" />
+  </ItemGroup>
+
   <ItemGroup>
     <Compile Update="GitHubResources.Designer.cs">
       <DesignTime>True</DesignTime>