miri no longer builds after rust-lang/rust#79196

[rust-highfive]

Hello, this is your friendly neighborhood mergebot.
After merging PR #79196, I observed that the tool miri has failing tests.
A follow-up PR to the repository https://github.com/rust-lang/miri is needed to fix the fallout.

cc @RalfJung, do you think you would have time to do the follow-up work?
If so, that would be great!

[m-ou-se]

Error log: https://github.com/rust-lang-ci/rust/runs/1429657808?#step:24:8507

error: Undefined Behavior: scalar size mismatch: expected 8 bytes but got 4 bytes instead
   --> /checkout/library/std/src/sys/unix/fs.rs:107:9
    |
107 | /         syscall! {
108 | |             fn statx(
109 | |                 fd: c_int,
110 | |                 pathname: *const libc::c_char,
...   |
114 | |             ) -> c_int
115 | |         }
    | |_________^ scalar size mismatch: expected 8 bytes but got 4 bytes instead