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

[Valentin Clement バレンタイン クレメン via cfe-commits]

clementval wrote:

 > Clang/Flang disagree whether 'seq' and 'self' can appear on the same serial-loop construct. I see no prose to support this?

`seq` and `self` are not in the same set for `serial loop` and seems to be accepted. https://godbolt.org/z/dzdoE3xKr

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