[patch] "single step" atomic instruction sequences as a whole.

[Luis Machado]

Ulrich,

I had the following errors on HEAD. It might be due to my specific build
environment though.

spu-linux-nat.c: In function 'fetch_ppc_register':
spu-linux-nat.c:64: error: 'PPC_PTRACE_PEEKUSR_3264' undeclared (first
use in this function)
spu-linux-nat.c:64: error: (Each undeclared identifier is reported only
once
spu-linux-nat.c:64: error: for each function it appears in.)
spu-linux-nat.c: In function 'fetch_ppc_memory_1':
spu-linux-nat.c:97: error: 'PPC_PTRACE_PEEKTEXT_3264' undeclared (first
use in this function)
spu-linux-nat.c: In function 'store_ppc_memory_1':
spu-linux-nat.c:116: error: 'PPC_PTRACE_POKEDATA_3264' undeclared (first
use in this function)

The only change i made to the SPU architecture ws the return type from
the spu_software_single_step function.

Regards,
Luis