os: TestRootDirFS failures on linux-mips64 and linux-mips64le

[mknyszek]

For example: https://build.golang.org/log/5d553b659dedaa835802a79cf1866ed511913cbf

CC @neild maybe?

[neild]

syscall.fstatat is busted on linux/mips64, since it passes a *Stat_t to a syscall that expects a *stat_t.

[gopherbot]

Change https://go.dev/cl/633280 mentions this issue: syscall, internal/syscall/unix: fix fstatat on linux/mips64

[gopherbot]

Change https://go.dev/cl/636836 mentions this issue: [release-branch.go1.24] syscall, internal/syscall/unix: fix fstatat on linux/mips64

[gopherbot]

Change https://go.dev/cl/637739 mentions this issue: internal/syscall/unix: apply fstatat fix to linux/mips64le