Without this patch, an `omp target exit data` before the runtime is
initialized produces a runtime error. This patch fixes that by
changing `__tgt_target_data_end_mapper` to call `CheckDeviceAndCtors`
like many other runtime routines.
Discussed at
<https://lists.llvm.org/pipermail/openmp-dev/2021-March/003920.html>.
Reviewed By: grokos
Differential Revision: https://reviews.llvm.org/D97907
Joel E. Denny