Make rust-intrinsic ABI unwindable

Stick `#[rustc_nounwind]` to all except `const_eval_select` to undo the
change for all other intrinsics.

compiler/rustc_middle/src/ty/layout.rs

@@ -1226,10 +1226,11 @@ pub fn fn_can_unwind(tcx: TyCtxt<'_>, fn_def_id: Option<DefId>, abi: SpecAbi) ->
         | AvrNonBlockingInterrupt
         | CCmseNonSecureCall
         | Wasm
-        | RustIntrinsic
         | PlatformIntrinsic
         | Unadjusted => false,
-        Rust | RustCall | RustCold => tcx.sess.panic_strategy() == PanicStrategy::Unwind,
+        Rust | RustCall | RustCold | RustIntrinsic => {
+            tcx.sess.panic_strategy() == PanicStrategy::Unwind
+        }
     }
 }
 

library/core/src/ffi/mod.rs

@@ -615,12 +615,15 @@ impl<'f> Drop for VaListImpl<'f> {
 extern "rust-intrinsic" {
     /// Destroy the arglist `ap` after initialization with `va_start` or
     /// `va_copy`.
+    #[rustc_nounwind]
     fn va_end(ap: &mut VaListImpl<'_>);
 
     /// Copies the current location of arglist `src` to the arglist `dst`.
+    #[rustc_nounwind]
     fn va_copy<'f>(dest: *mut VaListImpl<'f>, src: &VaListImpl<'f>);
 
     /// Loads an argument of type `T` from the `va_list` `ap` and increment the
     /// argument `ap` points to.
+    #[rustc_nounwind]
     fn va_arg<T: sealed_trait::VaArgSafe>(ap: &mut VaListImpl<'_>) -> T;
 }

library/core/src/ptr/mod.rs

@@ -1371,6 +1371,7 @@ pub const unsafe fn write<T>(dst: *mut T, src: T) {
     // as `intrinsics::copy_nonoverlapping` is a wrapper function.
     extern "rust-intrinsic" {
         #[rustc_const_stable(feature = "const_intrinsic_copy", since = "1.63.0")]
+        #[rustc_nounwind]
         fn copy_nonoverlapping<T>(src: *const T, dst: *mut T, count: usize);
     }