Changes to dotnet-compile

- Split dotnet-compile into dotnet-compile and
dotnet-compile-{compiler}
- We still need to figure out the protocol and responsibility
but this change adds the needed indirection so that compilers can do
their thing.
- Updated the bootstrap script and kept the commands since we need
them to bootstrap the world until we get updates.

#52

src/Microsoft.DotNet.Tools.Compiler.Csc/Program.cs

@@ -0,0 +1,52 @@
+using System;
+using System.IO;
+using Microsoft.Dnx.Runtime.Common.CommandLine;
+using Microsoft.DotNet.Cli.Utils;
+
+namespace Microsoft.DotNet.Tools.Compiler.Csc
+{
+    public class Program
+    {
+        public static void Main(string[] args)
+        {
+            DebugHelper.HandleDebugSwitch(ref args);
+
+            var app = new CommandLineApplication();
+            app.Name = "dotnet compile csc";
+            app.FullName = "CSharp compiler";
+            app.Description = "CSharp Compiler for the .NET Platform";
+            app.HelpOption("-h|--help");
+
+            var responseFileArg = app.Argument("<CONFIG>", "The response file to pass to the compiler.");
+
+            app.OnExecute(() =>
+            {
+                // Execute CSC!
+                var result = RunCsc($"-noconfig @\"{responseFileArg.Value}\"")
+                    .ForwardStdErr()
+                    .ForwardStdOut()
+                    .RunAsync()
+                    .Result;
+
+                return result.ExitCode;
+            });
+
+            app.Execute(args);
+        }
+
+        private static Command RunCsc(string cscArgs)
+        {
+            // Locate CoreRun
+            string hostRoot = Environment.GetEnvironmentVariable("DOTNET_CSC_PATH");
+            if (string.IsNullOrEmpty(hostRoot))
+            {
+                hostRoot = AppContext.BaseDirectory;
+            }
+            var corerun = Path.Combine(hostRoot, Constants.CoreRunName);
+            var cscExe = Path.Combine(hostRoot, "csc.exe");
+            return File.Exists(corerun) && File.Exists(cscExe)
+                ? Command.Create(corerun, $@"""{cscExe}"" {cscArgs}")
+                : Command.Create("csc", cscArgs);
+        }
+    }
+}