And it's just to get the definition of size_t.
To get the one that match your machine, you can replace that include statement with the result of
echo | gcc -E -xc -include 'stddef.h' - | grep size_t
Just remove the internal/ directory in the header files in the internal directory.
Add the lib directory at the root of the project.
Copy dds.so, libmdl_sdk.so, and nv_freeimage.so from the MDL Linux libraries into the lib directory.