Restore the test checks for wider_reduce_into_iter

The current minimum support is for LLVM 17.

tests/codegen/simd/simd-wide-sum.rs

@@ -51,8 +51,8 @@ pub fn wider_reduce_iter(x: Simd<u8, N>) -> u16 {
 #[no_mangle]
 // CHECK-LABEL: @wider_reduce_into_iter
 pub fn wider_reduce_into_iter(x: Simd<u8, N>) -> u16 {
-    // FIXME: It would be nice if this was exactly the same as the above tests,
-    // but at the time of writing this comment, that didn't happen on LLVM main.
-    // CHECK: call i16 @llvm.vector.reduce.add
+    // CHECK: zext <16 x i8>
+    // CHECK-SAME: to <16 x i16>
+    // CHECK: call i16 @llvm.vector.reduce.add.v16i16(<16 x i16>
     x.to_array().into_iter().map(u16::from).sum()
 }