[clang] [Offloading][NFC] Move creation of offloading entries from OpenMP (PR #70116)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> Can this stuff really be generic?

Obviously flags are going to be target dependent, but the actual form, generation, and iteration of these can be generic. The idea is to put them all into a single section such that we can filter out the ones that apply to whatever runtime so they can all live in the same section and re-use all the same code.

https://github.com/llvm/llvm-project/pull/70116