I'm using a Unix system. I run the configure script and then make but the build stops because the file "config/Makefile.def" could not be found.
This means that the configure script has failed to create the necessary makefile definitions. There could be several reasons for this. Look at the output of the configure program. If you see a line like:checking whether cross-compiling... yes
then your compiler seems to be producing code which cannot be executed. You could be using a very old compiler or some (shared) libraries could not be located. It has been reported that some GNU C++ installations install shared libraries in non-standard places (e.g. "/opt/gnu/lib") and that environment variables must be set before the compiler can be used (e.g. the LD_LIBRARY_PATH environment variable).