[nativeaot] Don't overwrite $(LinkNativeDependsOn) property

[grendello]

The $(LinkNativeDependsOn) property is used by the LinkNative target to list its dependency targets. Unfortunately, its value is unconditionally overwritten in Microsoft.NETCore.Native.targets, making it impossible for 3rd parties to add custom dependency targets to the LinkNative target.

Change the code to make sure that previous value of the property is preserved.

[Copilot]

Pull Request Overview

This PR fixes an issue in the NativeAOT build integration where the $(LinkNativeDependsOn) property was being unconditionally overwritten, preventing third-party customizations from adding custom dependency targets to the LinkNative target.

• Preserves existing values in $(LinkNativeDependsOn) while adding the required IlcCompile dependency

[dotnet-policy-service]

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[teo-tsirpanis]

Isn't it better to use BeforeTargets="LinkNative" to have a target run before LinkNative? My understanding is that the ***DependsOn properties is a relic of the past, before MSBuild added support for BeforeTargets and AfterTargets.

[MichalStrehovsky]

Isn't it better to use BeforeTargets="LinkNative" to have a target run before LinkNative? My understanding is that the ***DependsOn properties is a relic of the past, before MSBuild added support for BeforeTargets and AfterTargets.

Looking at the rest of the SDK, it's more common not to provide overridability, but if this is useful, I don't see a problem with this.