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

[Johannes Doerfert via llvm-commits]

jdoerfert wrote:

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



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