Use libc pipe2 instead of raw pipe2 syscall on Linux

[bjorn3]

The latter doesn't work in miri.

[NobodyXu]

rust-lang/rust#127154 the anonymous pipe feature is going through stabilisation process now, if it is merged and debian trixie uses the latest rustc with it stablised, then we could save a lot of code

[hanna-kruppe]

std::io::pipe() is on track to be be stable in Rust 1.87 but Debian Trixie has entered "toolchain freeze" two weeks ago, which I believe prevents further rustc updates. On the bright side, Rust 1.85 is in Trixie. That includes the MSRV-aware resolver as well as the 2024 edition which makes the MSRV-aware resolver the default. Hopefully this makes a more liberal MSRV policy than "whatever Debian stable ships" acceptable -- those who need to support Debian stable won't have to actively fight Cargo to exclude newer versions of dependencies with higher MSRV.