The entire "unix" part was updated with OSF/1 source code, with patches here and there of Free and NetBSD codebase. But especially when compiling code that was

The entire "unix" part was updated with OSF/1 source code, with patches here and there of Free and NetBSD codebase. But especially when compiling code that was written in C for "modern BSD" (Net/Free/Open) you can easily hit the part where userland etc. is OSF/1 branched off BSD 4.3/4.4 and simply does not include things people "assume" are present on BSD (like the more advanced linked list and tree macros)