Update eta-build to support rts-clean target
Update eta-build to support rts-clean target

rahulmutt/ghcvm,AlexeyRaga/eta,AlexeyRaga/eta,rahulmutt/ghcvm,pparkkin/eta,AlexeyRaga/eta,rahulmutt/ghcvm,pparkkin/eta,pparkkin/eta,pparkkin/eta,rahulmutt/ghcvm,AlexeyRaga/eta,pparkkin/eta,rahulmutt/ghcvm,AlexeyRaga/eta