tests: allow trunc/select instructions to be missing

On LLVM 20, these instructions already get eliminated, which at least
partially satisfies a TODO. I'm not talented enough at using FileCheck
to try and constrain this further, but if we really want to we could
copy an LLVM 20 specific version of this test that would restore it to
being CHECK-NEXT: insertvalue ...

@rustbot label: +llvm-main

tests/codegen/try_question_mark_nop.rs

@@ -1,22 +1,24 @@
 //@ compile-flags: -O -Z merge-functions=disabled --edition=2021
 //@ only-x86_64
 // FIXME: Remove the `min-llvm-version`.
-//@ min-llvm-version: 19
+//@ revisions: NINETEEN TWENTY
+//@[NINETEEN] min-llvm-version: 19
+//@[NINETEEN] ignore-llvm-version: 20-99
+//@[TWENTY] min-llvm-version: 20
 
 #![crate_type = "lib"]
 #![feature(try_blocks)]
 
 use std::ops::ControlFlow::{self, Break, Continue};
 use std::ptr::NonNull;
 
-// FIXME: The `trunc` and `select` instructions can be eliminated.
 // CHECK-LABEL: @option_nop_match_32
 #[no_mangle]
 pub fn option_nop_match_32(x: Option<u32>) -> Option<u32> {
     // CHECK: start:
-    // CHECK-NEXT: [[TRUNC:%.*]] = trunc nuw i32 %0 to i1
-    // CHECK-NEXT: [[FIRST:%.*]] = select i1 [[TRUNC]], i32 %0
-    // CHECK-NEXT: insertvalue { i32, i32 } poison, i32 [[FIRST]]
+    // NINETEEN-NEXT: [[TRUNC:%.*]] = trunc nuw i32 %0 to i1
+    // NINETEEN-NEXT: [[FIRST:%.*]] = select i1 [[TRUNC]], i32 %0
+    // CHECK-NEXT: insertvalue { i32, i32 } poison, i32 %0, 0
     // CHECK-NEXT: insertvalue { i32, i32 }
     // CHECK-NEXT: ret { i32, i32 }
     match x {