Naive short circuiting implementation for user panics and results. (#167)

* Add panic and result catching

* exit process on panic and user runtime error

* Complete initial implementation

lib/clif-backend/src/signal/mod.rs

@@ -2,9 +2,9 @@ use crate::relocation::{TrapData, TrapSink};
 use crate::trampoline::Trampolines;
 use hashbrown::HashSet;
 use libc::c_void;
-use std::sync::Arc;
+use std::{cell::Cell, sync::Arc};
 use wasmer_runtime_core::{
-    backend::{ProtectedCaller, Token},
+    backend::{ProtectedCaller, Token, UserTrapper},
     error::RuntimeResult,
     export::Context,
     module::{ExportIndex, ModuleInfo, ModuleInner},
@@ -24,6 +24,19 @@ pub use self::unix::*;
 #[cfg(windows)]
 pub use self::windows::*;
 
+thread_local! {
+    pub static TRAP_EARLY_DATA: Cell<Option<String>> = Cell::new(None);
+}
+
+pub struct Trapper;
+
+impl UserTrapper for Trapper {
+    unsafe fn do_early_trap(&self, msg: String) -> ! {
+        TRAP_EARLY_DATA.with(|cell| cell.set(Some(msg)));
+        trigger_trap()
+    }
+}
+
 pub struct Caller {
     func_export_set: HashSet<FuncIndex>,
     handler_data: HandlerData,
@@ -118,6 +131,10 @@ impl ProtectedCaller for Caller {
             })
             .collect())
     }
+
+    fn get_early_trapper(&self) -> Box<dyn UserTrapper> {
+        Box::new(Trapper)
+    }
 }
 
 fn get_func_from_index(