[clang] [OpenACC] Switch Clang to use the Flang 'appertainment' rules for cla… (PR #135372)

[Erich Keane via cfe-commits]

erichkeane wrote:

Note: No real reason to review this quite yet?  I'm still going to do a bunch of work on tablegen to no  longer use the FLANG generated things by generating clang ones that are similar, so a lot of the Appertainment.cpp file is going to change.

https://github.com/llvm/llvm-project/pull/135372