You should configure NetSolve before attempting to compile the GridRPC library. Compiling all of NetSolve isn't necessary to compile the GridRPC client library, however the NetSolve client library will be automatically built first if it hasn't been built already. Therefore, to build the GridRPC API, from the NETSOLVE_ROOT, it should suffice to simply type:
UNIX> make gridrpc
This creates a file named $NETSOLVE_ROOT/lib/$NETSOLVE_ARCH/libnsgrpc.a as well as the NetSolve client library if necessary (named $NETSOLVE_ROOT/lib/$NETSOLVE_ARCH/libnetsolve.a).