Convert 'Init' to MSBuild.

build_projects/dotnet-cli-build/SetEnvVar.cs

@@ -0,0 +1,22 @@
+using System;
+using Microsoft.Build.Framework;
+using Microsoft.Build.Utilities;
+
+namespace Microsoft.DotNet.Cli.Build
+{
+    public class SetEnvVar : Task
+    {
+        [Required]
+        public string Name { get; set; }
+
+        [Required]
+        public string Value { get; set; }
+
+        public override bool Execute()
+        {
+            Environment.SetEnvironmentVariable(Name, Value);
+
+            return true;
+        }
+    }
+}