[PATCH] powerpc/Makefiles: Fix clang/llvm build

[Anton Blanchard]

Hi Michael,

> This breaks GCC 4.6.3 at least, which we still support:
> 
>   Assembler messages:
>   Error: invalid switch -mpower8
>   Error: unrecognized option -mpower8
>   ../scripts/mod/empty.c:1:0: fatal error: error closing -: Broken
> pipe

Yuck. We have POWER8 instructions in our assembly code, and a toolchain
that doesn't understand the -mpower8 flag, but has support for
power8 instructions.

This is what I see on clang with -mpower7:

/tmp/sstep-2afa55.s:7584: Error: unrecognized opcode: `lbarx'
/tmp/sstep-2afa55.s:7626: Error: unrecognized opcode: `stbcx.'
/tmp/sstep-2afa55.s:8077: Error: unrecognized opcode: `lharx'
/tmp/sstep-2afa55.s:8140: Error: unrecognized opcode: `stbcx.'

Nick: any suggestions?

Thanks,
Anton