[spu] Fix C++ build problems

ChangeLog:

	* spu-linux-nat.c (spu_bfd_iovec_pread): Add pointer cast for C++.
	(spu_bfd_open): Likewise.

gdbserver/ChangeLog:

	* spu-low.c (fetch_ppc_register): Cast PowerPC-Linux-specific value
	used as first ptrace argument to PTRACE_TYPE_ARG1 for C++.
	(fetch_ppc_memory_1, store_ppc_memory_1): Likewise.