HI Praveen,
I assume you want to write RTlinux application here.
You will have to use the SDK provided by the RTlinux vendor, There is every possibility that it is an eclipse configured for the RTlinux.
If I assume you want to write a RTOS all together then you can simply write it in C and compile it with GCC but you have to pass "-nostdlib -nostdinc -nostartfiles -nodefaultlibs -fno-builtin"
It will be much easier if you go to windriver website and have a look at the Linux (RT linux) offering , They actually bough RT linux from FSM. The free evaluation version is quite easy to learn and substantial help is available