Welcome to LQ. .. ..
May be, you are using the "original LEACH Makefile"
in ns-allinone-2.27/ns-2.27 ? It has some wrong paths.
Please have a look at the "1-LEACH-Makefile-modified(.txt)" here
> > post # 92. ( You will have to edit to the used compiler : CC= , CXX = .
And please read the threads tagged 'leach' :
> 'Search by Tag' , "Tag" = leach
Good luck !