-Wundef warning in boost/interprocess/detail/workaround.hpp

[pdimov]

One more, sorry:

In file included from ./boost/interprocess/allocators/allocator.hpp:23:
./boost/interprocess/detail/workaround.hpp:89:9: error: '_XOPEN_SOURCE' is not defined, evaluates to 0 [-Werror,-Wundef]
   89 |    #if (_XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L)
      |         ^

This one only appears on macOS.

https://github.com/boostorg/unordered/actions/runs/20694312818/job/59416261269#step:12:1457