[clang] [coroutine] Create coroutine body in the correct eval context (PR #78589)

[via cfe-commits]

https://github.com/cor3ntin approved this pull request.

LGTM, thanks!
Please give a chance  to @ChuanqiXu9 to look at it before merging

https://github.com/llvm/llvm-project/pull/78589