Android arm64 cross-build fails with current main and NDK r29

Version

Current upstream main at 1e9fd9544ef38e6e36ca1d5ab7af3bab5b20496d

Platform

Android 11 target, arm64, API 30
Android NDK r29
Linux x86_64 build host

What steps will reproduce the bug?

On an unmodified checkout of main:

./android-configure /path/to/android-ndk-r29 30 arm64
make

What do you see instead?

The Android configure script assigns the Android target compiler to CC and
CXX. That compiler is also used for host-side tools such as ICU and V8
generators. The Android zlib target includes the NDK CPU-feature header but
does not include the corresponding sources/android/cpufeatures/cpu-features.c
implementation, which causes the Android CPU feature symbols to be missing
from the link.

Android cross builds can also reach V8 host-tool configurations where the
required POSIX trap-handler sources are not selected. Android trap-handler
activation must remain disabled; the required source selection is a separate
build concern.

Expected behavior

android-configure should select separate host and target compilers, and an
Android arm64 build should complete without requiring local absolute paths or
hand-edited generated files when using NDK r29.

Current status

The follow-up changes are kept separately reviewable:

1. #65772 separates host and
   target compilers.
2. #65773 compiles the Android
   NDK CPU feature implementation through a checked-in wrapper.
3. #65774 selects the required V8
   POSIX and host simulator sources while keeping Android trap-handler support
   disabled.

Validation with NDK r29, Android API 30, and arm64 completed successfully. The
resulting Node binary also passed basic zlib, crypto, Intl, WebAssembly, and
SharedArrayBuffer runtime checks on Android 11.

The issue remains open pending upstream review and CI completion for the three
follow-up pull requests.

Validation notes

Runtime loading used the matching NDK libc++_shared.so alongside the binary
and did not require a system-image change.

The earlier NDK r27d std::atomic_ref compatibility observation is retained
only as historical context. PR #65775 was closed because an ordinary simdutf
API is not an equivalent atomic fallback for SharedArrayBuffer access; it is
not part of the current fix.

The changes are intended to be generic and do not depend on a particular
Android system-image integration, device serial number, or checkout path.

Start with android-configure and the Android zlib build path, then inspect host-side ICU/V8 generator selection and the sources/android/cpufeatures/cpu-features.c implementation. Review PRs #65772, #65773, and #65774 before reproducing with NDK r29, API 30, and arm64. Done means the build completes and the listed Android runtime checks pass.