[llvm] [OpenMP] Port the OpenMP device runtime to direct C++ compilation (PR #123673)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

Works AFIACT once I stripped out the buggy member to ptr handling, but definitely needs more tests and hopefull the other two dependencies can be landed uncontroversially.

https://github.com/llvm/llvm-project/pull/123673