llvm JIT to another target code?

Hi,
I am using llvm on cell,
there are two different cores on cell, one is PPU and the other is SPU.
but the JIT'ed code is always for PPU.
I am trying to emit code for SPU through JIT.

but I face the following questions:
1. I've trace the JIT code, but I still cant find exactly where JIT allocate
PPU as it's target.
    is it done at make time?

2. I am trying to add an option that is -march=cellSPU to lli, how can I do
that?

Can anyone give me some tips or tell me which document I should study.
thanks.