[msbuild] Only validate the Info.plist values if we're actually creating an app manifest.

msbuild/Xamarin.MacDev.Tasks.Core/Tasks/CompileAppManifestTaskBase.cs

@@ -72,6 +72,8 @@ namespace Xamarin.MacDev.Tasks
 		public string SdkVersion { get; set; }
 
 		public string TargetArchitectures { get; set; }
+
+		public bool Validate { get; set; }
 		#endregion
 
 		protected TargetArchitecture architectures;

msbuild/Xamarin.Shared/Xamarin.Shared.targets

@@ -337,6 +337,7 @@ Copyright (C) 2018 Microsoft. All rights reserved.
 			SdkIsSimulator="$(_SdkIsSimulator)"
 			SdkVersion="$(_SdkVersion)"
 			DebugIPAddresses="$(_DebugIPAddresses)"
+			Validate="$(_CreateAppManifest)"
 			>
 		</CompileAppManifest>
 	</Target>

msbuild/Xamarin.iOS.Tasks.Core/Tasks/CompileAppManifestTaskCore.cs

@@ -286,6 +286,9 @@ namespace Xamarin.iOS.Tasks
 
 		void Validation (PDictionary plist)
 		{
+			if (!Validate)
+				return;
+
 			var supportsIPhone = (supportedDevices & IPhoneDeviceType.IPhone) != 0
 			                     || supportedDevices == IPhoneDeviceType.NotSet;
 			var supportsIPad = (supportedDevices & IPhoneDeviceType.IPad) != 0;