Update landlock.h
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When allocating a struct of a specific size, but only filling in some members, everything should be zeroed out first (before, e.g., passing the struct to the kernel). This was not an issue until now, since the relevant API structures are always fully filled, however, with an upcoming Landlock struct change, this is required: when not zeroing the memory, some random values would be passed to the kernel, resulting in an error (this could only be reproduced on GHC 8.10 and 9.0, though, it looks like more recent versions have `alloca` return zeroed memory). Where before `Foreign.Marshal.Utils.with` was used to get a pointer to a structure, `with0` is introduced which basically does the same (`alloca`, `poke`, run the callback), but uses `fillBytes` to zero out the `alloca`ted memory before `poke`ing the `Storable` in place.
Copied from Linux 6.8, ref e8f897f4afef0031fe618a8e94127a0934896aba. See: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/plain/include/uapi/linux/landlock.h?id=e8f897f4afef0031fe618a8e94127a0934896aba
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