[ Answer by Bela and Robertl ] 

                  SCO cc            GDS               EGCS or GCC >= 2.8.0
              ==============  ===============   ==============================
      Make things to go into .so
              -belf -KPIC         -belf -fpic             -fpic

      Make a .so
              -belf -G            -belf -G                -G

      Use a .so
              -belf               -belf                   

Everything is identical between SCO's cc and GDS except the spelling 
of the "generate position-independent code" option.

GCC 2.8.0 and EGCS 1.0 default to ELF, making the flag to emit ELF 
unnecessary.