Changes to SWI-cpp.h

It seems that g++ 12 has problems with SWI-cpp.h – discussion is here: Problems compiling Rocksdb
I intend to install g++ 12 and see if I can reproduce the problems … it takes a while to download and build the compiler, so I don’t know when I’ll be able to do this.

EDIT: I could not reproduce the problem after building and installing g++ 12