[llvm] [Offload] Move `/openmp/libomptarget` to `/offload` (PR #75125)

[Jan Patrick Lehr via llvm-commits]

jplehr wrote:

> Added `set(LIBOMP_HAVE_OMPT_SUPPORT ${LIBOMP_HAVE_OMPT_SUPPORT} PARENT_SCOPE)` to the CMake as suggested, also rebased it on trunk.

I just did another local test, and the OMPT tests are still shown as `UNSUPPORTED`. I think @dhruvachak is right in that we need that additional logic to actually enable OMPT support in `offload`.

https://github.com/llvm/llvm-project/pull/75125