Fix nvptx-safe-naming.rs test on LLVM 21

This is now printed on the same line. Use NEXT/SAME depending on
the LLVM version.

Author: nikic

tests/assembly/nvptx-safe-naming.rs

@@ -1,6 +1,9 @@
 //@ assembly-output: ptx-linker
 //@ compile-flags: --crate-type cdylib -Z unstable-options -Clinker-flavor=llbc
 //@ only-nvptx64
+//@ revisions: LLVM20 LLVM21
+//@ [LLVM21] min-llvm-version: 21
+//@ [LLVM20] max-llvm-major-version: 20
 
 #![feature(abi_ptx)]
 #![no_std]
@@ -15,7 +18,8 @@ extern crate breakpoint_panic_handler;
 #[no_mangle]
 pub unsafe extern "ptx-kernel" fn top_kernel(a: *const u32, b: *mut u32) {
     // CHECK:      call.uni (retval0),
-    // CHECK-NEXT: [[IMPL_FN]]
+    // LLVM20-NEXT: [[IMPL_FN]]
+    // LLVM21-SAME: [[IMPL_FN]]
     *b = deep::private::MyStruct::new(*a).square();
 }