Implement the output dropping for windows, too

Author: oli-obk

src/machine.rs

@@ -291,6 +291,9 @@ pub struct Evaluator<'mir, 'tcx> {
 
     /// Failure rate of compare_exchange_weak, between 0.0 and 1.0
     pub(crate) cmpxchg_weak_failure_rate: f64,
+
+    /// Corresponds to -Zmiri-drop-stdout-stderr and doesn't write the output but acts as if it succeeded.
+    pub(crate) drop_stdout_stderr: bool,
 }
 
 impl<'mir, 'tcx> Evaluator<'mir, 'tcx> {
@@ -344,6 +347,7 @@ impl<'mir, 'tcx> Evaluator<'mir, 'tcx> {
             tracked_alloc_ids: config.tracked_alloc_ids.clone(),
             check_alignment: config.check_alignment,
             cmpxchg_weak_failure_rate: config.cmpxchg_weak_failure_rate,
+            drop_stdout_stderr: config.drop_stdout_stderr,
         }
     }
 

src/shims/windows/dlsym.rs

@@ -75,7 +75,9 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriEvalContextExt<'mir, 'tcx
                     use std::io::{self, Write};
 
                     let buf_cont = this.read_bytes_ptr(buf, Size::from_bytes(u64::from(n)))?;
-                    let res = if handle == -11 {
+                    let res = if this.machine.drop_stdout_stderr {
+                        Ok(buf_cont.len())
+                    } else if handle == -11 {
                         io::stdout().write(buf_cont)
                     } else {
                         io::stderr().write(buf_cont)