An executable RTS is a system executable file that requires the first entry point to be specified at run time. C and C++ programs can exist within callable shared objects; you do not have to create an executable RTS for this.
If you require, you can create an executable RTS using cob. For example, the following command creates an executable RTS that contains the same level of functionality as the default run-time system ($COBDIR/bin/rts32 or $COBDIR/bin/rts32_t) that also includes the C subroutines held in the file subprogs.c:
cob -xo rts.new subprogs.c -e ""
At run time the dynamically loadable program myapp could then be run with the command line:
./rts.new myapp
Specifying the cob option -e "" causes the system executable to be built so that the executable file's entry point must be specified at run time.