i'm trying to test out the llvm backend on OS X with ghc head plus llvm 3.5

and i'm seeing stuff like  the following. 
Could someone help me undestand whats going on?!


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*** Clang (Assembler):
clang -m64 -fno-stack-protector -DTABLES_NEXT_TO_CODE -I. -fno-common -U__PIC__ -D__PIC__ -Qunused-arguments -x assembler -c /var/folders/py/wgp_hj9d2rl3cx48yym_ynj00000gn/T/ghc89553_0/ghc89553_7.s -o TestFetch.o

/var/folders/py/wgp_hj9d2rl3cx48yym_ynj00000gn/T/ghc89553_0/ghc89553_7.s:3:2:
     error: unknown directive
            .macosx_version_min 10, 0
            ^

<no location info>:
    Error running clang! you need clang installed to use theLLVM backend
    (or GHC tried to execute clang incorrectly)