added make clean to llvm build process
added make clean to llvm build process

weld-project/weld,sppalkia/weld,weld-project/weld,rahulpalamuttam/weld,weld-project/weld,rahulpalamuttam/weld,sppalkia/weld,sppalkia/weld,sppalkia/weld,weld-project/weld,rahulpalamuttam/weld,rahulpalamuttam/weld,rahulpalamuttam/weld,weld-project/weld,sppalkia/weld