[clang] [clang] Fix GNU spellings of lifetimebound/lifetime_capture_by (PR #192070)

[Zeyi Xu via cfe-commits]

zeyi2 wrote:

Thanks all for the feedback and the additional questions here.

My original goal for this PR was fairly narrow: to fix the current GNU/standard inconsistency for the member-function postfix spelling.

>From the discussion so far, it seems this may be touching a broader modeling question around these attributes. So I am not sure whether this PR should try to address that design question or whether it would be preferable to keep this PR narrowly scoped to the current behavior gap and discuss the larger attribute-modeling issue separately.

I would be happy to take either direction, but I wanted to check which scope would be preferred before pushing this further :)

https://github.com/llvm/llvm-project/pull/192070