An executabe is already linked.
Any executable consists of ONE main program and zero to several
subprograms.
You can not have more than one main program in an executable.
Your objective seems that you wish to be able to execute the three
separate codes from one executable.
You can only do this by two methods
a) Writing one main program that calls any of ypur three executable by
name as "daughter" programs. OR
b) Build a new main program with the blocks of code from the other
programs as subroutines themselves.