Fix using `crash-handler` under Miri

[repi]

This resolves a Linux compile error when building projects for Miri that uses the crash-handler crate.

Belive Miri shims pthread_create so we can't do it ourselves, and as the purpose of running with Miri is to run tests in an interpreted sandbox we don't need the crash handler there but it is the easiest if it can compile to avoid having special configurations in all usages.

Here is an example of the Miri compile error one ran into without this (from cargo +nightly miri nextest run -p ark-svc-auto-proxy):

error: found `pthread_create` symbol definition that clashes with a built-in shim
   --> /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/unix/thread.rs:87:19
    |
87  |         let ret = libc::pthread_create(&mut native, &attr, thread_start, p as *mut _);
    |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ found `pthread_create` symbol definition that clashes with a built-in shim
    |
help: the `pthread_create` symbol is defined here
   --> /home/repi/.cargo/registry/src/index.crates.io-6f17d22bba15001f/crash-handler-0.6.0/src/unix/pthread_interpose.rs:52:1
    |
52  | / pub extern "C" fn pthread_create(
53  | |     thread: *mut libc::pthread_t,
54  | |     attr: *const libc::pthread_attr_t,
55  | |     main: pthread_main_t,
...   |
107 | |     result
108 | | }
    | |_^
    = note: BACKTRACE (of the first span):
    = note: inside `std::sys::unix::thread::Thread::new` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/sys/unix/thread.rs:87:19: 87:86
    = note: inside `std::thread::Builder::spawn_unchecked_::<'_, '_, [closure@test::run_test::run_test_inner::{closure#1}], ()>` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/thread/mod.rs:563:17: 568:18
    = note: inside `std::thread::Builder::spawn_unchecked::<'_, [closure@test::run_test::run_test_inner::{closure#1}], ()>` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/thread/mod.rs:457:32: 457:62
    = note: inside `std::thread::Builder::spawn::<[closure@test::run_test::run_test_inner::{closure#1}], ()>` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/std/src/thread/mod.rs:389:18: 389:41
    = note: inside `test::run_test::run_test_inner` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/test/src/lib.rs:599:19: 599:80
    = note: inside `test::run_test` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/test/src/lib.rs:642:28: 648:10
    = note: inside `test::run_tests::<[closure@test::run_tests_console::{closure#2}]>` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/test/src/lib.rs:380:31: 380:98
    = note: inside `test::run_tests_console` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/test/src/console.rs:329:5: 329:70
    = note: inside `test::test_main` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/test/src/lib.rs:139:15: 139:55
    = note: inside `test::test_main_static` at /home/repi/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/test/src/lib.rs:158:5: 158:40
    = note: inside `main`

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to previous error