[openmp] Set up .arcconfig to point to new Diffusion OMP repository
We want to automatically copy the appropriate mailing list
for review requests to the openmp repository.
For context, see the proposal and discussion here:
Similar to D40179, I set up a new Diffusion repository with callsign
"OMP" for OpenMP:
This explicitly updates openmp's .arcconfig to point to the new
OMP repository in Diffusion, which will let us use Herald rule H272
to automatically subscribe openmp-commits to review requests.
Reviewers: hans, grokos, Hahnfeld
Reviewed By: grokos
Subscribers: sammccall, klimek, openmp-commits
Differential Revision: https://reviews.llvm.org/D40499