[build] Copy NDK redistributables when creating runtime packs

[simonrozsival]

Context

make prepare currently copies selected Android NDK files into bin/<Configuration>/lib/runtimes/redist, even though those files are only consumed when producing runtime packs. This creates an approximately 58 MB configuration- and checkout-local staging directory in every prepared worktree.

The NDK itself is already stored in the shared Android toolchain directory, so the intermediate copy is unnecessary.

Changes

• Remove _CopyNdkRedistributables from Android SDK provisioning.
• Add the NDK toolchain metadata to AndroidSupportedTargetJitAbi.
• Expose the selected NDK files through a reusable _AndroidGetNdkRedistributables target.
• Copy those files directly from $(AndroidNdkDirectory) into local unpacked runtime packs.
• Use the same direct NDK inputs when creating runtime-pack NuGet packages.
• Remove the now-unused runtime redist staging property.

Mono runtime packs receive the five Android system-library stubs. CoreCLR and NativeAOT runtime packs additionally receive the CRT objects, libc++, compiler-rt, and libunwind, preserving the existing payload.

Validation

• make prepare succeeds without creating bin/Debug/lib/runtimes/redist.
• _AndroidGetNdkRedistributables selects 44 existing files: 11 for each supported RID.
• make all succeeds.
• Local runtime packs contain 5 NDK assets for Mono and 11 for CoreCLR/NativeAOT.
• Representative android-arm64 Mono and CoreCLR NuGet runtime packs build successfully and contain the expected files under runtimes/android-arm64/native.

[Copilot]

Pull request overview

This PR refactors how Android NDK redistributable assets are sourced for runtime pack creation, removing the configuration-local “redist” staging directory created during make prepare and instead selecting/copying the needed NDK files directly from $(AndroidNdkDirectory) when producing runtime packs and runtime-pack NuGets.

Changes:

• Removes _CopyNdkRedistributables from Android SDK provisioning and deletes the unused _RuntimeRedistDirName property.
• Introduces a reusable _AndroidGetNdkRedistributables target and extends AndroidSupportedTargetJitAbi metadata to support selecting the right NDK files per RID.
• Updates runtime pack directory population and runtime-pack NuGet packing to consume @(_AndroidNdkRedistributable) directly.

Show a summary per file

File	Description
src/native/native.targets	Uses _AndroidGetNdkRedistributables and copies NDK redistributables directly into local unpacked runtime packs.
src/androidsdk/androidsdk.targets	Stops copying NDK redistributables during SDK install/provisioning (make prepare).
Configuration.props	Removes the now-unused _RuntimeRedistDirName property and imports NDK build script definitions.
build-tools/scripts/Ndk.targets	Adds _AndroidGetNdkRedistributables to compute the per-RID NDK redistributable file list.
build-tools/scripts/Ndk.projitems	Adds NDK toolchain metadata (prefix/arch/unwind dir) to AndroidSupportedTargetJitAbi items.
build-tools/create-packs/Microsoft.Android.Runtime.proj	Packs NDK system/toolchain assets directly from @(_AndroidNdkRedistributable) when building runtime-pack NuGets.

Review details

Suppressed comments (1)

src/native/native.targets:379

• 💡 suggestion performance — _CopyToPackDirs performs a large Copy into the local packs directory but still has no Inputs/Outputs, so MSBuild will consider it out-of-date on every build. Since this target is in the Build dependency chain, it can add noticeable overhead even when SkipUnchangedFiles="true". Consider making it incremental (e.g., move input item computation to a helper ...Inputs target and use a stamp file output).

  <Target Name="_CopyToPackDirs"
          DependsOnTargets="_AndroidGetNdkRedistributables">
    <PropertyGroup>
      <_RuntimePackName Condition=" '$(CMakeRuntimeFlavor)' == 'MonoVM' ">Mono</_RuntimePackName>
      <_RuntimePackName Condition=" '$(CMakeRuntimeFlavor)' == 'CoreCLR' ">CoreCLR</_RuntimePackName>
      <_RuntimePackName Condition=" '$(CMakeRuntimeFlavor)' == 'NativeAOT' ">NativeAOT</_RuntimePackName>
    </PropertyGroup>

    <ItemGroup>
      <_RuntimePackFiles Include="$(OutputPath)\%(AndroidSupportedTargetJitAbi.AndroidRID)\*"
                         AndroidRID="%(AndroidSupportedTargetJitAbi.AndroidRID)"
                         AndroidRuntime="$(CMakeRuntimeFlavor)"
                         RuntimePackName="$(_RuntimePackName)" />
      <_RuntimePackFiles Include="@(_AndroidNdkRedistributable)"
                         Condition=" '%(_AndroidNdkRedistributable.Kind)' == 'System' "
                         AndroidRID="%(_AndroidNdkRedistributable.AndroidRID)"
                         AndroidRuntime="$(CMakeRuntimeFlavor)"
                         RuntimePackName="$(_RuntimePackName)" />
    </ItemGroup>

    <ItemGroup Condition=" '$(CMakeRuntimeFlavor)' == 'CoreCLR' Or '$(CMakeRuntimeFlavor)' == 'NativeAOT' ">
      <_RuntimePackFiles Include="@(_AndroidNdkRedistributable)"
                         Condition=" '%(_AndroidNdkRedistributable.Kind)' == 'Toolchain' "
                         AndroidRID="%(_AndroidNdkRedistributable.AndroidRID)"
                         AndroidRuntime="$(CMakeRuntimeFlavor)"
                         RuntimePackName="$(_RuntimePackName)" />
    </ItemGroup>

    <Copy
        SourceFiles="%(_RuntimePackFiles.Identity)"
        DestinationFolder="$(MicrosoftAndroidPacksRootDir)Microsoft.Android.Runtime.%(_RuntimePackFiles.RuntimePackName).$(AndroidApiLevel).%(_RuntimePackFiles.AndroidRID)\$(AndroidPackVersion)\runtimes\%(_RuntimePackFiles.AndroidRID)\native"
        SkipUnchangedFiles="true" />
  </Target>

• Files reviewed: 6/6 changed files
• Comments generated: 1
• Review effort level: Lite