[test] Adjust IRGen test to succeed both on main and rebranch
* `getelementptr inbounds` -> `getelementptr inbounds nuw`. This
attribute was introduced in
https://github.com/llvm/llvm-project/pull/107257 (llvm-project). Match
it using a wildcard regex, since it is irrelevant to this test.
* Both the syntax and relative order of the LLVM `nocapture` parameter
attribute changed in https://github.com/llvm/llvm-project/pull/123181.
Adjust the FileCheck patterns to expect both syntaxes/orders. This
change is temporary and will be cleaned up once rebranch is merged
into main.
