handle SIGQUIT (#5744)

* handle sigquit

* fix clippy

crates/nu-protocol/src/engine/engine_state.rs

@@ -75,6 +75,8 @@ pub struct EngineState {
     pub config: Config,
     #[cfg(feature = "plugin")]
     pub plugin_signatures: Option<PathBuf>,
+    #[cfg(not(windows))]
+    sig_quit: Option<Arc<AtomicBool>>,
 }
 
 pub const NU_VARIABLE_ID: usize = 0;
@@ -106,6 +108,8 @@ impl EngineState {
             config: Config::default(),
             #[cfg(feature = "plugin")]
             plugin_signatures: None,
+            #[cfg(not(windows))]
+            sig_quit: None,
         }
     }
 
@@ -713,6 +717,21 @@ impl EngineState {
 
         self.num_files() - 1
     }
+
+    #[cfg(not(windows))]
+    pub fn get_sig_quit(&self) -> &Option<Arc<AtomicBool>> {
+        &self.sig_quit
+    }
+
+    #[cfg(windows)]
+    pub fn get_sig_quit(&self) -> &Option<Arc<AtomicBool>> {
+        &None
+    }
+
+    #[cfg(not(windows))]
+    pub fn set_sig_quit(&mut self, sig_quit: Arc<AtomicBool>) {
+        self.sig_quit = Some(sig_quit)
+    }
 }
 
 /// A temporary extension to the global state. This handles bridging between the global state and the