test: add new incremental case

This is similar to the old `llvm/shift_right_plus_left` case, which was
disabled by 1b1c78c. The case is not enabled on the LLVM backend, since
incremental compilation support for this backend is a work in progress
and is tracked by #21165. It passes on the x86_64-linux target with the
self-hosted backend.

Resolves: #12288
6e56bc1096mlugg committed on 11/11/2024, 12:22:55 PMparentca12e4f
1 file changedLine totals unavailable