https://gitlab.synchro.net/main/sbbs/-/commit/b725fe4be5473b171599b996
Modified Files:
src/build/Common.gmake src/xpdev/CMakeLists.txt
Log Message:
It's spelt _POSIX_C_SOURCE

Since this doesn't work, we're clearly not relying on it, so remove
it.

Reported by: jrtc27 via IRC
--- SBBSecho 3.24-Linux
* Origin: Vertrauen - [vert/cvs/bbs].synchro.net (1:103/705)