Ninja was already included in the android_build container, so there's no
need to put it in the Ephemeral packages, which only meant that it was
removed at the end of the LLVM build.
Also, add the usual image tag header at the top of
build-android-x86_64-llvm.sh.
Signed-off-by: Valentine Burley <valentine.burley@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34180>
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