tests: codegen-llvm: Allow additional LLVM attributes in bpf-alu32

The LLVM backend now emits `noundef zeroext` on `i8` return values and
`noundef` on `i8` parameters. Update the FileCheck pattern to match
those, and any possible future attributes.

Author: vadorovsky

tests/codegen-llvm/bpf-alu32.rs

@@ -5,7 +5,7 @@
 
 #[no_mangle]
 #[target_feature(enable = "alu32")]
-// CHECK: define i8 @foo(i8 returned %arg) unnamed_addr #0
+// CHECK: define {{.*}}i8 @foo(i8 {{.*}}returned %arg) unnamed_addr #0
 pub unsafe fn foo(arg: u8) -> u8 {
     arg
 }