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

[Peter Klausler via flang-commits]

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

The old-school idiom for this would be `(_POSIX_SOURCE+0)`.

You don't need the parentheses with `defined`.

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