text: In order to use the C code in these directories, you should first
  modify / setup the file config/LocalMakefileConfig.mk, which is
  included by the main Makefiles and allows you to overwrite the
  settings from config/Makefile.mk.
  
  Once this is done, run make.
  
  You must then use the install targets to copy / link the resulting
  shared libraries with their full paths into the "luatex/lib"
  subdirectory of the directory where your TeX executable resides. For
  instance, if the luatex program is in 
  
  /usr/texbin
  
  then you would put SimpleDemoC.so into
  
  /usr/texbin/lib/luatex/lua/pgf/gd/examples/c
  
  
  Due to bugs in the LuaTeX code, you currently need to append the paths
  of the libraries to their name as done in the Makefiles.
  
  Note that, currently, the Makefile will link the Lua library
  statically into the shared graph drawing library (at least on
  MacOS). This is conceptually wrong and, indeed, a lot of effort was
  need to avoid having LuaTeX crash on a TeX run because of two Lua
  libraries being used simultaneously. It works, but hopefully, in the
  fututure, this will be fixed. 