so there are several approaches, but first of all I have to ask:
Did you made already kernel project for your target device?
If Yes go to the rootfs ->lib folder and check is this library persists there. if no-> find where it is (somewhere in /usr/local/DigiEL-5.0) and copy it. after that make kernel project update rootfs in the digi module, and should works
I wandering why for hello world project such library is searched for?
why don't you try
export path :
gandalf@damage:~/workspace/$ export PATH=$PATH:/usr/local/DigiEL-5.0/usr/bin
gandalf@damage:~/workspace/$ arm-linux-gcc helloworld.c -o helloworld
gandalf@damage:~/workspace/$ scp helloworld root@targetIPadress:/tmp
in the shell of Digi module
/ # ./tmp/helloworld