This was likely copied from amd64, but the layout of the struct differs
slightly between these platforms. This fixes spurious `unsupported sigaction
flag 0xXXXXXXXX` messages when executing some Linux binaries on arm64.
Linux struct definition: https://github.com/torvalds/linux/blob/34816d20f173a90389c8a7e641166d8ea9dce70a/include/uapi/asm-generic/signal.h#L104