CMake's bundled libarchive can request the ARM64 BCJ filter when
extracting 7-Zip archives that use the ARM64 method. The bundled
liblzma build already carries the ARM64 simple filter implementation,
but CMake's reduced build configuration did not enable it or compile
its source file.
Enable the ARM64 encoder and decoder declarations and include
liblzma/simple/arm64.c in the bundled liblzma build.
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