On a system where SWI-Prolog 5.4.7 has been configured with a simple `configure', this gives
$ /usr/local/bin/pl -dump-runtime-variables CC="gcc"; PLBASE="/usr/local/lib/pl-5.4.7"; PLARCH="i686-linux"; PLLIBS="-ldl -lreadline -lncurses -lm -lrt "; PLLIB="-lpl"; PLLDFLAGS="-export-dynamic -O3 -pthread"; PLSOEXT="so"; PLVERSION="50407"; PLSHARED="yes"; PLTHREADS="yes";
Instead, on a system where SWI-Prolog 5.4.7 has been configured with `./configure --disable-mt', the same command gives
$ /tmp/junk/bin/pl -dump-runtime-variables CC="gcc"; PLBASE="/tmp/junk/lib/pl-5.4.7"; PLARCH="i686-linux"; PLLIBS="-ldl -lreadline -lncurses -lm "; PLLIB=""; PLLDFLAGS="-export-dynamic -O3"; PLSOEXT="so"; PLVERSION="50407"; PLSHARED="yes"; PLTHREADS="no";
For some reason, PLLIB is now assigned the empty string. This makes `plld' fail miserably and, since I don't see any connection between multithreading and the observed behavior, I wonder if this is a bug. All the best,
Roberto