Under Ubuntu 64 bit I got
llc --version LLVM (http://llvm.org/): LLVM version 3.1 Optimized build with assertions. Built Oct 15 2012 (18:15:59). Defa
You're confusing your flags. clang's -march= wants a processor family. You probably meant to use clang -arch arm instead.
-march=
clang -arch arm