[llvm] [mlir] [OpenMP][IRBuilder] Handle `target ... nowait` when codegen targets host (PR #124720)

[Kareem Ergawy via llvm-commits]

ergawy wrote:

Ran `check-offload` locally and both reported tests run successfully for me. Also both are not `nowait` related. So not sure if these tests are flakey or something else I did wrong on my side:
```
PASS: libomptarget :: amdgcn-amd-amdhsa :: offloading/host_as_target.c (240 of 1002)
PASS: libomptarget :: amdgcn-amd-amdhsa :: mapping/declare_mapper_nested_mappers.cpp (55 of 1002)
```

https://github.com/llvm/llvm-project/pull/124720