[mtouch] It seems watchOS simulators can automatically choose the rig…

…ht architecture from fat apps.

So we can build a fat simulator app, and not depend on mlaunch copying in the
specific architecture at launch time.

A partial fix for xamarin/maccore#2411.

tools/common/Application.cs

@@ -336,6 +336,14 @@ public bool IsSimulatorBuild {
 			}
 		}
 
+		// It seems the watch simulator is able to correctly select which architecture to use
+		// for a fat executable, so limit ourselves to arch-specific executables anymore.
+		public bool ArchSpecificExecutable {
+			get {
+				return !IsWatchExtension;
+			}
+		}
+
 		public static int Concurrency => Driver.Concurrency;
 		public Version DeploymentTarget;
 		public Version SdkVersion;

tools/mtouch/Application.mtouch.cs

@@ -1092,7 +1092,7 @@ void BuildApp ()
 				link_tasks.AddRange (target.NativeLink (build_tasks));
 			}
 
-			if (IsDeviceBuild || Platform == ApplePlatform.MacCatalyst) {
+			if (IsDeviceBuild || Platform == ApplePlatform.MacCatalyst || !ArchSpecificExecutable) {
 				// If building for the simulator, the executable is written directly into the expected location within the .app, and no lipo/file copying is needed.
 				if (link_tasks.Count > 1) {
 					// If we have more than one executable, we must lipo them together.

tools/mtouch/Target.mtouch.cs

@@ -181,7 +181,7 @@ public IDictionary<Abi, string> Executables {
 			get {
 				if (executables == null) {
 					executables = new Dictionary<Abi, string> ();
-					if (App.IsSimulatorBuild) {
+					if (App.IsSimulatorBuild && App.ArchSpecificExecutable) {
 						// When using simlauncher, we copy the executable directly to the target directory.
 						// When not using the simlauncher, but still building for the simulator, we write the executable to a arch-specific app directory (if building for both 32-bit and 64-bit), or just the app directory (if building for a single architecture)
 						if (Abis.Count != 1)