[libomp] OpenMP 6.0 Device-Scope Environment Variables (#197191)
The patch introduces `_ALL` `_DEV` `_DEV_<id>` env var suffixes to the
LLVM's OpenMP host runtime `libomp`. The eligible-list env var currently
supports `OMP_NUM_THREADS`.
Assisted by Claude Opus 4.7 / Claude 4.6 Sonnet