For each type of system, the name of the appropriate s- header file is given. Changes merged, and may work. I have as yet no evidence of whether this problem, known in HP-UX, exists in other system V versions. A different s- file is used to enable the other interface. Emacs version 18 unexec is currently not working properly on 5.2.2.
Nobody knows why yet.
It is not yet known whether this applies to all machines running 5.2.2. Some versions of this system support ptys and BSD-style sockets. The standard C preprocessor generates xmakefile incorrectly. Versions 3 and earlier of V.4, on the Intel 386 and 860, had problems in the X11 libraries. If xemacs runs, your X11 library is new enough.