So I have figured out what you need to do to get the Simulink generated UDP code to compile on an ARM processor.
HostLib_Network.c has two sets of functions. Below is a snippet from HostLib_Network.c:
void CreateUDPInterface(void *hl)
{
#ifndef _USE_TARGET_UDP_
CreateHostLibrary(libName_Network, hl);
#else
CreateTargetUDPInterface(hl);
#endif
}
As you can see if _USE_TARGET_UDP_ is not defined then it uses a library name. If it is defined then it uses the OS's own UDP library.
So all you have to do is add the flag _USE_TARGET_UDP_ to your ARM compiler and it will compile and run fine.