[NativeAOT] Stop shipping libc++ archives in the runtime packs

[simonrozsival]

Contributes to #12139. Builds on #12523, which stopped linking libc++ into NativeAOT applications.

The NativeAOT runtime packs still ship libc++_static.a, libc++abi.a and libunwind.a even though nothing links them any more.

Why this needs a new item kind

_AndroidNdkRedistributable (in build-tools/scripts/Ndk.targets) tagged NDK files with just two kinds:

• System — libc.so, libdl.so, liblog.so, libm.so, libz.so — shipped to every runtime.
• Toolchain — crtbegin_so.o, crtend_so.o, libc++_static.a, libc++abi.a, libclang_rt.builtins-*.a, libunwind.a — shipped to CoreCLR and NativeAOT, since both do native linking.

NativeAOT still needs crtbegin_so.o, crtend_so.o and libclang_rt.builtins-*.a, so the Toolchain group cannot just be dropped for NativeAOT.

This adds a third kind, CplusPlus, for the three C++ archives, and ships it only for CoreCLR. Both packaging sites are updated:

• src/native/native.targets — the local bin/<Config>/lib/packs layout.
• build-tools/create-packs/Microsoft.Android.Runtime.proj — the shipped NuGet packs.

Size

Per ABI, removed from the NativeAOT runtime pack:

Archive	Size
libc++_static.a	15,182,348
libc++abi.a	3,125,348
libunwind.a	91,152
Total	18,398,848

Across android-arm, android-arm64 and android-x64 that is roughly 55 MB of pack content. This does not change application size — that was #12523 — but it shrinks what users restore.

Testing

Deleted each pack directory and regenerated it via _CopyToPackDirs, rather than checking a pack that could still contain stale files.

NativeAOT (android-arm64) — the three archives are gone, and everything NativeAOT links is still present:

crtbegin_so.o crtend_so.o libc.so libclang_rt.builtins-aarch64-android.a
libdl.so liblog.so libm.so libz.so
libnaot-android.debug-static-debug.a libnaot-android.debug.so
libnaot-android.release-static-release.a libnaot-android.release.so
libxa-java-interop-release.a

CoreCLR (android-arm64) — all three are still shipped:

crtbegin_so.o crtend_so.o libarchive-dso-stub.so libc.so
libc++_static.a libc++abi.a libclang_rt.builtins-aarch64-android.a
libdl.so liblog.so libm.so libunwind.a libz.so

Mono is unaffected — it only ever received the System kind.

[Copilot]

Pull request overview

This PR reduces the size of the shipped Android NativeAOT runtime packs by stopping the inclusion of libc++-related NDK archives (libc++_static.a, libc++abi.a, libunwind.a) that are no longer linked by NativeAOT. It does this by introducing a new NDK redistributable “Kind” (CplusPlus) and only packaging those assets for the CoreCLR runtime flavor.

Changes:

• Introduce a new _AndroidNdkRedistributable.Kind value CplusPlus for the three C++ archives.
• Update local pack staging (src/native/native.targets) to include CplusPlus assets only for CoreCLR.
• Update shipped NuGet runtime pack creation (Microsoft.Android.Runtime.proj) to include CplusPlus assets only for CoreCLR.

Show a summary per file

File	Description
src/native/native.targets	Adds CoreCLR-only inclusion of CplusPlus NDK archives when copying assets into the local runtime pack directory layout.
build-tools/scripts/Ndk.targets	Re-tags libc++/libunwind NDK archives from Toolchain to the new CplusPlus kind.
build-tools/create-packs/Microsoft.Android.Runtime.proj	Adds CoreCLR-only inclusion of CplusPlus NDK archives when creating the shipped runtime pack NuGets.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Lite

[simonrozsival]

Consolidated into #12523 to reduce the depth of the #12546 stack.

No code changed: the commits from this PR are now part of #12523 unmodified, and the resulting tree is byte-identical. This PR sat directly on top of #12523 and touched the same files, so reviewing them together is easier than reviewing the same file across two intermediate states.