Don't use MIRI_DEFAULT_ARGS to compile host crates

[ghost]

They (specifically, --cfg=miri) may cause procedural macros (and probably build scripts) to depend on Miri-only symbols, such as miri_resolve_frame.

This PR makes miri detect host crates inspecting the value of the MIRI_BE_RUSTC environment variable (target -> target crate, host -> host crate, other -> panic) and skip the insertion of MIRI_DEFAULT_ARGS if it's a host crate.

Fixes #1760

[ghost]

run-pass/concurrency/libc_pthread_cond.rs:

thread 'rustc' panicked at 'no callback found', src/thread.rs:714:55
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::option::expect_failed
   3: core::option::Option<T>::expect
             at /Users/runner/.rustup/toolchains/master/lib/rustlib/src/rust/library/core/src/option.rs:349:21
   4: miri::thread::EvalContextExt::run_timeout_callback
             at ./src/thread.rs:714:13
   5: miri::eval::eval_main::{{closure}}
             at ./src/eval.rs:230:21
   6: miri::eval::eval_main
             at ./src/eval.rs:218:38
   7: <miri::MiriCompilerCalls as rustc_driver::Callbacks>::after_analysis::{{closure}}
             at ./src/bin/miri.rs:53:40
   8: rustc_interface::passes::QueryContext::enter::{{closure}}
             at /Users/runner/.rustup/toolchains/master/lib/rustlib/src/rust/compiler/rustc_interface/src/passes.rs:755:42
   9: rustc_middle::ty::context::tls::enter_context::{{closure}}
             at /Users/runner/.rustup/toolchains/master/lib/rustlib/src/rust/compiler/rustc_middle/src/ty/context.rs:1726:50
  10: rustc_middle::ty::context::tls::set_tlv
             at /Users/runner/.rustup/toolchains/master/lib/rustlib/src/rust/compiler/rustc_middle/src/ty/context.rs:1710:9
  11: rustc_middle::ty::context::tls::enter_context
             at /Users/runner/.rustup/toolchains/master/lib/rustlib/src/rust/compiler/rustc_middle/src/ty/context.rs:1726:9
  12: rustc_interface::passes::QueryContext::enter
             at /Users/runner/.rustup/toolchains/master/lib/rustlib/src/rust/compiler/rustc_interface/src/passes.rs:755:9
  13: <miri::MiriCompilerCalls as rustc_driver::Callbacks>::after_analysis
             at ./src/bin/miri.rs:35:9
  14: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  15: rustc_span::with_source_map
  16: rustc_interface::interface::create_compiler_and_run
  17: scoped_tls::ScopedKey<T>::set

https://github.com/rust-lang/miri/runs/2289905504

🤔

[ghost]

That looks like a strange timer issue... I don't think it's related to this PR though.

[RalfJung]

It somehow managed to trigger this line

miri/src/thread.rs

Line 714 in 7b2e325

this.machine.threads.get_ready_callback().expect("no callback found");

That... should not be possible? We have some non-determinism somewhere...

[RalfJung]

This is great, thanks a lot. :-)
Can you squash the commits together a bit? Then I'll land it.

[ghost]

Squashed. 🚀

[RalfJung]

@bors r+
🚢

[bors]

📌 Commit 3dff1d4 has been approved by RalfJung

[bors]

⌛ Testing commit 3dff1d4 with merge 1ec52ab...

[bors]

☀️ Test successful - checks-actions
Approved by: RalfJung
Pushing 1ec52ab to master...