[offload] - Add omp as a dependency for clang-bootstrap-deps (#90793)

If openmp is on the LLVM_ENABLE_PROJECTS list and
offload is on LLVM_ENABLE_RUNTIMES list when using
CLANG_ENABLE_BOOTSTRAP, then the runtimes will be
configured before the openmp project. This will throw a cannot find
libomp.so dependency error. Add omp as a dependency when this is the
case. Update
offload cmake for detection of LIBOMP_HAVE_VERSION_SCRIPT.