Switch wasm from core intrinsic to LLVM intrinsic

In preparation for changes in rust-lang/rust#148291.

Author: purplesyringa

src/backend/itanium.rs

@@ -160,8 +160,12 @@ unsafe extern "C" fn cleanup(_code: i32, _ex: *mut Header) {
     );
 }
 
-#[cfg(not(target_arch = "wasm32"))]
 unsafe extern "C-unwind" {
+    #[cfg(target_arch = "wasm32")]
+    #[link_name = "llvm.wasm.throw"]
+    fn wasm_throw(tag: i32, ex: *mut u8) -> !;
+
+    #[cfg(not(target_arch = "wasm32"))]
     fn _Unwind_RaiseException(ex: *mut u8) -> !;
 }
 
@@ -183,6 +187,6 @@ unsafe fn raise(ex: *mut u8) -> ! {
     #[cfg(target_arch = "wasm32")]
     // SAFETY: Passthrough.
     unsafe {
-        core::arch::wasm32::throw::<0>(ex);
+        wasm_throw(0, ex);
     }
 }

src/backend/wasm.rs

@@ -18,7 +18,7 @@ unsafe impl ThrowByPointer for ActiveBackend {
     unsafe fn throw(ex: *mut Header) -> ! {
         // SAFETY: Wasm has no unwinder, so the pointer reaches `intercept` as-is.
         unsafe {
-            core::arch::wasm32::throw::<0>(ex.cast::<u8>().wrapping_add(1));
+            wasm_throw(0, ex.cast::<u8>().wrapping_add(1));
         }
     }
 
@@ -34,7 +34,7 @@ unsafe impl ThrowByPointer for ActiveBackend {
             // safe because it's indistinguishable from not catching it in the first place due to
             // Wasm EH being performed by the VM.
             unsafe {
-                core::arch::wasm32::throw::<0>(ex);
+                wasm_throw(0, ex.cast());
             }
         }
 
@@ -45,5 +45,10 @@ unsafe impl ThrowByPointer for ActiveBackend {
     }
 }
 
+unsafe extern "C-unwind" {
+    #[link_name = "llvm.wasm.throw"]
+    fn wasm_throw(tag: i32, ex: *mut u8) -> !;
+}
+
 #[repr(C, align(2))]
 pub struct Header;

src/lib.rs

@@ -191,7 +191,7 @@
 #![cfg_attr(backend = "seh", feature(fn_ptr_trait, std_internals))]
 #![cfg_attr(
     any(backend = "wasm", all(backend = "itanium", target_arch = "wasm32")),
-    feature(wasm_exception_handling_intrinsics)
+    feature(link_llvm_intrinsics)
 )]
 #![deny(unsafe_op_in_unsafe_fn)]
 #![warn(