Compile libsass for one platform at a time

Added an inline MSBuild task, which make use of a new CoreFX API
`System.Runtime.InteropServices.RuntimeInformation` to obtain OS
description and architecture information, then translates into
`LibSassPlatform` (Win32 or Win64 etc.).

Also added ability to cross compile, e.g. Win32 on 64-bit system.

Additional OSes will be added with .NET Core support.

Fixes sass#47.

Author: am11

Diff for: LibSass.NET.Tests/LibSass.NET.Tests.csproj

@@ -117,7 +117,7 @@
   </Target>
   <Target Name="AfterBuild">
     <Copy
-      SourceFiles="$(LibSassPath)libsass32.dll;$(LibSassPath)libsass64.dll"
+      SourceFiles="$(LibSassPath)libsass.dll"
       DestinationFolder="$(OutputPath)"
       SkipUnchangedFiles="true" />
   </Target>

Diff for: LibSass.NET/LibSass.NET.csproj

@@ -67,15 +67,54 @@
   <ItemGroup>
     <None Include="LibSass.Net.nuspec" />
     <None Include="libsassnet.targets" />
+    <None Include="packages.config" />
   </ItemGroup>
   <ItemGroup>
     <Reference Include="System" />
     <Reference Include="System.Runtime.Serialization" />
   </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <!-- Detect Platform -->
+  <UsingTask TaskName="OSVersionInformation" TaskFactory="CodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll">
+    <ParameterGroup>
+      <LibSassPlatform ParameterType="System.String" Output="true" />
+    </ParameterGroup>
+    <Task>
+      <Using Namespace="System.Reflection" />
+      <Code Type="Fragment" Language="cs"><![CDATA[
+          var assembly = Assembly.LoadFrom(@"..\packages\System.Runtime.InteropServices.RuntimeInformation.4.3.0\lib\net45\System.Runtime.InteropServices.RuntimeInformation.dll");
+          Type runtimeType = assembly.GetType("System.Runtime.InteropServices.RuntimeInformation");
+          var osDescription = runtimeType.GetProperty("OSDescription")
+                             .GetValue(null, null).ToString();
+          var osArchitecture = runtimeType.GetProperty("OSArchitecture")
+                              .GetValue(null, null).ToString();
+
+          if (osDescription.StartsWith("Microsoft Windows"))
+          {
+              if (osArchitecture == "X86")
+              {
+                  LibSassPlatform = "Win32";
+              }
+              else if (osArchitecture == "X64")
+              {
+                  LibSassPlatform = "Win64";
+              }
+          }
+        ]]></Code>
+    </Task>
+  </UsingTask>
+  <Target Name="GetOSIdentifiers" Condition=" '$(LibSassPlatform)' == '' ">
+    <OSVersionInformation>
+      <Output TaskParameter="LibSassPlatform" PropertyName="LibSassPlatform" />
+    </OSVersionInformation>
+  </Target>
   <!-- Build LibSass -->
-  <Target Name="AfterBuild">
-    <MSBuild Targets="Build" Projects="..\LibSass\win\libsass.sln" BuildInParallel="true" Properties="Configuration=$(Configuration);Platform=Win32;TargetName=libsass32;OutDir=$(OutputPath);IntDir=$(IntermediateOutputPath)" />
-    <MSBuild Targets="Build" Projects="..\LibSass\win\libsass.sln" BuildInParallel="true" Properties="Configuration=$(Configuration);Platform=Win64;TargetName=libsass64;OutDir=$(OutputPath);IntDir=$(IntermediateOutputPath)" />
+  <Target Name="AfterBuild" DependsOnTargets="GetOSIdentifiers">
+    <Message Text="Commencing build for platform: $(LibSassPlatform)" />
+
+    <!-- Windows -->
+    <MSBuild Projects="..\LibSass\win\libsass.sln" BuildInParallel="true"
+             Condition="'$(LibSassPlatform)' == 'Win32' or '$(LibSassPlatform)' == 'Win64'"
+             Properties="Configuration=$(Configuration);Platform=$(LibSassPlatform);OutDir=$(OutputPath);IntDir=$(IntermediateOutputPath)" />
   </Target>
 </Project>

Diff for: LibSass.NET/packages.config

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="NETStandard.Library" version="1.6.1" targetFramework="net40" />
+  <package id="System.Runtime.InteropServices.RuntimeInformation" version="4.3.0" targetFramework="net45" />
+</packages>

Diff for: contrib/LibSass.NET.Console/LibSass.NET.Console.csproj

@@ -51,7 +51,7 @@
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Target Name="AfterBuild">
     <Copy
-      SourceFiles="$(LibSassPath)libsass32.dll;$(LibSassPath)libsass64.dll"
+      SourceFiles="$(LibSassPath)libsass.dll"
       DestinationFolder="$(OutputPath)"
       SkipUnchangedFiles="true" />
   </Target>

Diff for: contrib/LibSass.NET.Web/LibSass.NET.Web.csproj

@@ -58,7 +58,7 @@
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <Target Name="AfterBuild">
     <Copy
-      SourceFiles="$(LibSassPath)libsass32.dll;$(LibSassPath)libsass64.dll"
+      SourceFiles="$(LibSassPath)libsass.dll"
       DestinationFolder="$(OutputPath)"
       SkipUnchangedFiles="true" />
   </Target>