use v12 msbuild on .net 4.5

Author: fsgit

src/fsharp/FSharp.Compiler.Service/FSharp.Compiler.Service.fsproj

@@ -596,11 +596,17 @@
     <Reference Include="System" />
     <Reference Include="System.Core" />
     <Reference Include="System.Xml" />
-    <Reference Include="Microsoft.Build.Framework" />
-    <Reference Include="Microsoft.Build.Engine" />
-    <Reference Include="Microsoft.Build" />
-    <Reference Include="Microsoft.Build.Utilities.v4.0" />
-    <Reference Include="Microsoft.Build.Tasks.v4.0" />
+    <Reference Include="Microsoft.Build.Framework" Condition=" '$(TargetFrameworkVersion)' == 'v4.0'" />
+    <Reference Include="Microsoft.Build.Engine" Condition=" '$(TargetFrameworkVersion)' == 'v4.0'" />
+    <Reference Include="Microsoft.Build" Condition=" '$(TargetFrameworkVersion)' == 'v4.0'" />
+    <Reference Include="Microsoft.Build.Utilities.v4.0" Condition=" '$(TargetFrameworkVersion)' == 'v4.0'" />
+    <Reference Include="Microsoft.Build.Tasks.v4.0" Condition=" '$(TargetFrameworkVersion)' == 'v4.0'" />
+    
+    <Reference Include="Microsoft.Build.Framework, Version=12.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition=" '$(TargetFrameworkVersion)' == 'v4.5'" />
+    <Reference Include="Microsoft.Build.Engine, Version=12.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition=" '$(TargetFrameworkVersion)' == 'v4.5'" />
+    <Reference Include="Microsoft.Build, Version=12.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a" Condition=" '$(TargetFrameworkVersion)' == 'v4.5'" />
+    <Reference Include="Microsoft.Build.Utilities.v12.0" Condition=" '$(TargetFrameworkVersion)' == 'v4.5'" />
+    <Reference Include="Microsoft.Build.Tasks.v12.0" Condition=" '$(TargetFrameworkVersion)' == 'v4.5'" />
     <Reference Include="FSharp.Core, Version=$(TargetFSharpCoreVersion), Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a">
       <Private>False</Private>
     </Reference>