[dotnet] Fix building universal apps using NativeAOT when the default…

… RuntimeIdentifiers value is set. Fixes #19391.

We need to set "UseCurrentRuntimeIdentifier=false", we must only set it for
the outer build for universal builds - when `RuntimeIdentifiers` is set - but
that means we can only do it *after* we set any default value for
`RuntimeIdentifiers`.

Fixes #19391 (comment).

dotnet/targets/Xamarin.Shared.Sdk.props

@@ -94,10 +94,6 @@
 		<!-- Tell .NET to skip sanity checks that trigger too eagerly for builds with multiple RuntimeIdentifiers -->
 		<AllowPublishAotWithoutRuntimeIdentifier Condition="'$(AllowPublishAotWithoutRuntimeIdentifier)' == '' And '$(_UseNativeAot)' == 'true'">true</AllowPublishAotWithoutRuntimeIdentifier>
 		<AllowSelfContainedWithoutRuntimeIdentifier Condition="'$(AllowSelfContainedWithoutRuntimeIdentifier)' == ''">true</AllowSelfContainedWithoutRuntimeIdentifier>
-
-		<!-- Prevent .NET from resolving runtime identifier for NativeAOT builds when building universal apps. -->
-		<UseCurrentRuntimeIdentifier Condition="'$(_UseNativeAot)' == 'true' And '$(RuntimeIdentifiers)' != '' And '$(RuntimeIdentifier)' == ''">false</UseCurrentRuntimeIdentifier>
-
 	</PropertyGroup>
 
 	<!-- Set the default RuntimeIdentifier if not already specified. -->
@@ -142,6 +138,9 @@
 	</PropertyGroup>
 
 	<PropertyGroup>
+		<!-- Prevent .NET from resolving runtime identifier for NativeAOT builds when building universal apps. -->
+		<UseCurrentRuntimeIdentifier Condition="'$(_UseNativeAot)' == 'true' And '$(RuntimeIdentifiers)' != '' And '$(RuntimeIdentifier)' == ''">false</UseCurrentRuntimeIdentifier>
+
 		<!-- See Xamarin.Shared.Sdk.Trimming.props for an explanation why we use CustomAfterDirectoryBuildTargets to compute trimming options -->
 		<CustomAfterDirectoryBuildTargets>$(CustomAfterDirectoryBuildTargets);$(MSBuildThisFileDirectory)Xamarin.Shared.Sdk.Trimming.props</CustomAfterDirectoryBuildTargets>
 	</PropertyGroup>

tests/dotnet/UnitTests/ProjectTest.cs

@@ -1744,6 +1744,7 @@ public void BuildMyNativeAotAppWithTrimAnalysisWarning (ApplePlatform platform,
 		[TestCase (ApplePlatform.MacOSX, "osx-x64", "Release")]
 		[TestCase (ApplePlatform.MacOSX, "osx-arm64;osx-x64", "Debug")]
 		[TestCase (ApplePlatform.MacOSX, "osx-arm64;osx-x64", "Release")]
+		[TestCase (ApplePlatform.MacOSX, "", "Release")]
 		[TestCase (ApplePlatform.MacCatalyst, "maccatalyst-arm64", "Debug")]
 		[TestCase (ApplePlatform.MacCatalyst, "maccatalyst-arm64", "Release")]
 		[TestCase (ApplePlatform.MacCatalyst, "maccatalyst-arm64;maccatalyst-x64", "Debug")]