[flang-commits] [flang] [flang] allow _POSIX_SOURCE to be defined without a value (PR #78179)

[Yi Wu via flang-commits]

https://github.com/yi-wu-arm approved this pull request.

Don't know much about AIX but a `define(_POSIX_SOURCE)` would guarantee that it will work when define with and without a value, with the exception of 0.
I assume that there are no cases where it is defined as 0? Normally it should follow the yyyymm format like `200809L`.

https://github.com/llvm/llvm-project/pull/78179