Either clone this repository recursively:

git clone --recursive https://github.com/ampl/plugins.git

or, after cloning, check out the submodules:

git submodule update --init

To generate build files using cmake, for Linux/Unix/OSX systems (change 64 to 32 if a 32 bits build is needed):

mkdir build
cd build
cmake .. -DARCH=64

On Windows, with Visual Studio 2017+:

mkdir build
cd build
cmake .. 

add -A Win32 to the cmake statement to generate 32 bits libraries.