[flang-commits] [flang] [flang] Build a dedicated fir-test-opt for testing (PR #123473)

[Michał Górny via flang-commits]

mgorny wrote:

Updated as requested. I've also had to add it to the following two tests:

```
  Flang :: HLFIR/assign-side-effects.fir
  Flang :: HLFIR/memory-effects.fir
```

https://github.com/llvm/llvm-project/pull/123473