[msbuild] Don't inject our existing build logic into the *DependsOn variables when building using net5.

dotnet/targets/Xamarin.Shared.Sdk.props

@@ -4,6 +4,8 @@
   <Import Project="Xamarin.Shared.Sdk.Versions.props" />
 
   <PropertyGroup>
+    <!-- Set to true when using the Microsoft.<platform>.Sdk NuGet. This is used by pre-existing/shared targets to tweak behavior depending on build system -->
+    <_UsingXamarinSdk>true</_UsingXamarinSdk>
     <!-- This is the location of the Microsoft.<platform>.Sdk NuGet (/usr/local/share/dotnet/sdk/<version>/Sdks/Microsoft.[iOS/tvOS/watchOS/macOS].Sdk) -->
     <_XamarinSdkRootDirectory>$([MSBuild]::NormalizePath('$(MSBuildThisFileDirectory)', '..'))\</_XamarinSdkRootDirectory>
   </PropertyGroup>

msbuild/Xamarin.Mac.Tasks/Xamarin.Mac.Common.targets

@@ -96,7 +96,7 @@ Copyright (C) 2014 Xamarin. All rights reserved.
 		<_ACTool_BundleResourceCache>$(IntermediateOutputPath)actool\_BundleResourceWithLogicalName.items</_ACTool_BundleResourceCache>
 	</PropertyGroup>
 
-	<PropertyGroup>
+	<PropertyGroup Condition="'$(_UsingXamarinSdk)' != 'true'">
 		<BuildDependsOn>
 			BuildOnlySettings;
 			_CollectBundleResources;
@@ -162,7 +162,7 @@ Copyright (C) 2014 Xamarin. All rights reserved.
 
 	<Target Name="Codesign" Condition="'$(_CanOutputAppBundle)' == 'true'" DependsOnTargets="$(CodesignDependsOn)" />
 
-	<PropertyGroup>
+	<PropertyGroup Condition="'$(_UsingXamarinSdk)' != 'true'">
 		<CleanDependsOn>
 			$(CleanDependsOn);
 			_CleanAppBundle;

msbuild/Xamarin.Mac.Tasks/Xamarin.Mac.ObjCBinding.Common.targets

@@ -28,7 +28,7 @@ Copyright (C) 2014 Xamarin Inc. All rights reserved.
 	<Import Project="$(MSBuildThisFileDirectory)Xamarin.Mac.msbuild.targets"/>
 
 	<!-- Add our own pre-build steps -->
-	<PropertyGroup>
+	<PropertyGroup Condition="'$(_UsingXamarinSdk)' != 'true'">
 		<BuildDependsOn>
 			BuildOnlySettings;
 			_CreateGeneratedSourcesDir;
@@ -38,7 +38,7 @@ Copyright (C) 2014 Xamarin Inc. All rights reserved.
 	</PropertyGroup>
 
 	<!-- Add our own Clean steps -->
-	<PropertyGroup>
+	<PropertyGroup Condition="'$(_UsingXamarinSdk)' != 'true'">
 		<CleanDependsOn>
 			_CleanGeneratedSources;
 			$(CleanDependsOn)

msbuild/Xamarin.iOS.Tasks.Core/Xamarin.iOS.Common.targets

@@ -263,7 +263,7 @@ Copyright (C) 2013-2016 Xamarin. All rights reserved.
 	</Target>
 
 	<!-- Insert our app bundle generation step -->
-	<PropertyGroup>
+	<PropertyGroup Condition="'$(_UsingXamarinSdk)' != 'true'">
 		<BuildDependsOn>
 			BuildOnlySettings;
 			PrepareForBuild;

msbuild/Xamarin.iOS.Tasks.Core/Xamarin.iOS.ObjCBinding.Common.targets

@@ -32,7 +32,7 @@ Copyright (C) 2013-2016 Xamarin Inc. All rights reserved.
 	</PropertyGroup>
 
 	<!-- Add our own pre-build steps -->
-	<PropertyGroup>
+	<PropertyGroup Condition="'$(_UsingXamarinSdk)' != 'true'">
 		<BuildDependsOn>
 			BuildOnlySettings;
 			_CreateGeneratedSourcesDir;
@@ -42,7 +42,7 @@ Copyright (C) 2013-2016 Xamarin Inc. All rights reserved.
 	</PropertyGroup>
 
 	<!-- Add our own Clean steps -->
-	<PropertyGroup>
+	<PropertyGroup Condition="'$(_UsingXamarinSdk)' != 'true'">
 		<CleanDependsOn>
 			_CleanGeneratedSources;
 			$(CleanDependsOn)