Bring Host build into separate project

build_projects/dotnet-host-build/Program.cs

@@ -0,0 +1,17 @@
+using Microsoft.DotNet.Cli.Build.Framework;
+
+namespace Microsoft.DotNet.Host.Build
+{
+    public class Program
+    {
+        public static int Main(string[] args)
+        {
+            DebugHelper.HandleDebugSwitch(ref args);
+
+            return BuildSetup.Create(".NET Core Host")
+                .UseStandardGoals()
+                .UseAllTargetsFromAssembly<Program>()
+                .Run(args);
+        } 
+    }
+}