Auto merge of #111769 - saethlin:ctfe-backtrace-ctrlc, r=RalfJung

Print a backtrace in const eval if interrupted

Demo:
```rust
#![feature(const_eval_limit)]
#![const_eval_limit = "0"]

const OW: u64 = {
    let mut res: u64 = 0;
    let mut i = 0;
    while i < u64::MAX {
        res = res.wrapping_add(i);
        i += 1;
    }
    res
};

fn main() {
    println!("{}", OW);
}
```
```
╭ ➜ ben@archlinux:~/rust
╰ ➤ rustc +stage1 spin.rs
^Cerror[E0080]: evaluation of constant value failed
 --> spin.rs:8:33
  |
8 |         res = res.wrapping_add(i);
  |                                 ^ Compilation was interrupted

note: erroneous constant used
  --> spin.rs:15:20
   |
15 |     println!("{}", OW);
   |                    ^^

note: erroneous constant used
  --> spin.rs:15:20
   |
15 |     println!("{}", OW);
   |                    ^^
   |
   = note: this note originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to previous error

For more information about this error, try `rustc --explain E0080`.
```

Author: bors

src/bin/miri.rs

@@ -364,6 +364,10 @@ fn main() {
     let args = rustc_driver::args::raw_args(&early_dcx)
         .unwrap_or_else(|_| std::process::exit(rustc_driver::EXIT_FAILURE));
 
+    // Install the ctrlc handler that sets `rustc_const_eval::CTRL_C_RECEIVED`, even if
+    // MIRI_BE_RUSTC is set.
+    rustc_driver::install_ctrlc_handler();
+
     // If the environment asks us to actually be rustc, then do that.
     if let Some(crate_kind) = env::var_os("MIRI_BE_RUSTC") {
         // Earliest rustc setup.

src/concurrency/thread.rs

@@ -3,12 +3,13 @@
 use std::cell::RefCell;
 use std::collections::hash_map::Entry;
 use std::num::TryFromIntError;
-use std::sync::atomic::{AtomicBool, Ordering::Relaxed};
+use std::sync::atomic::Ordering::Relaxed;
 use std::task::Poll;
 use std::time::{Duration, SystemTime};
 
 use either::Either;
 
+use rustc_const_eval::CTRL_C_RECEIVED;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def_id::DefId;
 use rustc_index::{Idx, IndexVec};
@@ -1045,21 +1046,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     /// Run the core interpreter loop. Returns only when an interrupt occurs (an error or program
     /// termination).
     fn run_threads(&mut self) -> InterpResult<'tcx, !> {
-        static SIGNALED: AtomicBool = AtomicBool::new(false);
-        ctrlc::set_handler(move || {
-            // Indicate that we have ben signaled to stop. If we were already signaled, exit
-            // immediately. In our interpreter loop we try to consult this value often, but if for
-            // whatever reason we don't get to that check or the cleanup we do upon finding that
-            // this bool has become true takes a long time, the exit here will promptly exit the
-            // process on the second Ctrl-C.
-            if SIGNALED.swap(true, Relaxed) {
-                std::process::exit(1);
-            }
-        })
-        .unwrap();
-        let this = self.eval_context_mut();
+       let this = self.eval_context_mut();
         loop {
-            if SIGNALED.load(Relaxed) {
+            if CTRL_C_RECEIVED.load(Relaxed) {
                 this.machine.handle_abnormal_termination();
                 std::process::exit(1);
             }