Failure on NetBSD

[larseggert]

See https://github.com/mozilla/mtu/actions/runs/13576683480/job/37954428439?pr=94#step:6:1692

  error[E0463]: can't find crate for `profiler_builtins`
    |
    = note: the compiler may have been built without the profiler runtime

This is with a stable toolchain installed via rustup: https://github.com/mozilla/mtu/actions/runs/13576683480/job/37954428439?pr=94#step:6:1507

[taiki-e]

This is the same issue as rust-lang/rust#79556.

There are several solutions:

• Send PR that enables profiler_builtins on x86_64 netbsd to rust-lang/rust.
• Use custom toolchain with profiler_builtins enabled.
• Use nightly toolchain + -Z build-std. (Supported since Allow injecting a profiler runtime into #![no_core] crates rust-lang/rust#133369)