Bring Host build into separate project

build_projects/Microsoft.DotNet.Cli.Build.Framework/TargetAttribute.cs

@@ -0,0 +1,24 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Microsoft.DotNet.Cli.Build.Framework
+{
+    [AttributeUsage(AttributeTargets.Method, AllowMultiple = false, Inherited = false)]
+    public class TargetAttribute : Attribute
+    {
+        public string Name { get; set; }
+        public IEnumerable<string> Dependencies { get; }
+
+        public TargetAttribute()
+        {
+            Dependencies = Enumerable.Empty<string>();
+        }
+
+        // Attributes can only use constants, so a comma-separated string is better :)
+        public TargetAttribute(params string[] dependencies)
+        {
+            Dependencies = dependencies;
+        }
+    }
+}