Add explicit Miri support to libpanic_unwind

src/libcore/intrinsics.rs

@@ -1348,6 +1348,11 @@ extern "rust-intrinsic" {
     /// See documentation of `<*const T>::offset_from` for details.
     #[cfg(not(bootstrap))]
     pub fn ptr_offset_from<T>(ptr: *const T, base: *const T) -> isize;
+
+    /// Internal hook used by Miri to implement unwinding.
+    /// Perma-unstable: do not use
+    #[cfg(not(bootstrap))]
+    pub fn miri_start_panic(data: *mut (dyn crate::any::Any + Send)) -> !;
 }
 
 // Some functions are defined here because they accidentally got made