Make it buildable using the new CMake-based build system

[rla]

SWI-Prolog switched recently to CMake-based build system. New instructions based on it need to be written. It seems like the build command should be:

cd src
mkdir build
cmake -DCMAKE_TOOLCHAIN_FILE=~/emsdk/emscripten/1.38.11/cmake/Modules/Platform/Emscripten.cmake \
  -DCMAKE_BUILD_TYPE=Release \
  -DZLIB_LIBRARY=~/zlib-1.2.11/libz.a \
  -DZLIB_INCLUDE_DIR=~/zlib-1.2.11 \
  -G "Unix Makefiles" ..

The paths of the toolchain file and zlib location have to adjusted for the versions.

[rla]

It does seem like the zlib location has to be a full path, so:

cd src
mkdir build
cd build
cmake -DCMAKE_TOOLCHAIN_FILE=$HOME/emsdk/emscripten/1.38.11/cmake/Modules/Platform/Emscripten.cmake \
  -DCMAKE_BUILD_TYPE=Release \
  -DZLIB_LIBRARY=$HOME/zlib-1.2.11/libz.a \
  -DZLIB_INCLUDE_DIR=$HOME/zlib-1.2.11 \
  -G "Unix Makefiles" ..
make VERBOSE=1