[mtouch] A few adjustments after allowing multiple root assemblies.

* Remove the MT0008 test, since the error will never be shown again.
* Check non-existent root assemblies and report MT0018 instead of MT0007 if
  they look like command-line arguments.
* Collect all MT0018/MT0007 errors before reporting any of them.

tests/mtouch/MTouch.cs

@@ -448,17 +448,6 @@ namespace Xamarin
 			}
 		}
 
-		[Test]
-		public void MT0008 ()
-		{
-			using (var mtouch = new MTouchTool ()) {
-				mtouch.CreateTemporaryAppDirectory ();
-				mtouch.CustomArguments = new string [] { "foo.exe", "bar.exe" };
-				mtouch.AssertExecuteFailure (MTouchAction.BuildSim, "build");
-				mtouch.AssertError (8, "You should provide one root assembly only, found 2 assemblies: 'foo.exe', 'bar.exe'");
-			}
-		}
-
 		[Test]
 		public void MT0015 ()
 		{

tools/mtouch/Application.cs

@@ -1102,11 +1102,24 @@ namespace Xamarin.Bundler {
 			if (EnableAsmOnlyBitCode)
 				LLVMAsmWriter = true;
 
+			List<Exception> exceptions = null;
 			foreach (var root in RootAssemblies) {
-				if (!File.Exists (root))
-					throw new MonoTouchException (7, true, "The root assembly '{0}' does not exist", root);
+				if (File.Exists (root))
+					continue;
+
+				if (exceptions == null)
+					exceptions = new List<Exception> ();
+
+				if (root [0] == '-' || root [0] == '/') {
+					exceptions.Add (ErrorHelper.CreateError (18, "Unknown command line argument: '{0}'", root));
+				} else {
+					exceptions.Add (ErrorHelper.CreateError (7, "The root assembly '{0}' does not exist", root));
+				}
 			}
-			
+			if (exceptions?.Count > 0)
+				throw new AggregateException (exceptions);
+
+
 			if (no_framework)
 				throw ErrorHelper.CreateError (96, "No reference to Xamarin.iOS.dll was found.");
 

tools/mtouch/error.cs

@@ -16,7 +16,7 @@ namespace Xamarin.Bundler {
 	//					MT0005	<unused>
 	//					MT0006	There is no devel platform at '{0}', use --platform=PLAT to specify the SDK
 	//					MT0007	The root assembly '{0}' does not exist
-	//					MT0008	You should provide one root assembly only, found {0} assemblies: '{1}'
+	//					MT0008	<unused>
 	//					MT0009	Error while loading assemblies: {0}
 	//					MT0010	Could not parse the command line arguments: {0}
 	//					MT0011	{0} was built against a more recent runtime ({1}) than Xamarin.iOS supports