This patch fixes lowering for the num_teams, num_threads and thread_limit
clauses when inside of a target region and compiling for the host device.

The current approach requires these to be attached to the parent MLIR
omp.target operation. However, some incorrect checks based on the
`evalHasSiblings()` helper function would result in these clauses being
attached to the `omp.teams` or `omp.parallel` operation instead, triggering
a verifier error.

In this patch, these checks are updated to stop breaking when lowering
combined `target teams [X]` constructs. Also, the `genTeamsClauses()` function
is fixed to avoid processing num_teams and thread_limit twice, which probably
resulted from a recent merge.