submodules: updates for ARM builds

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
GNUmakefile: if nvcc is unavailable, assume non-CUDA build

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
nbody_CPU_NEON: unbreak building as C

Enough with the const & references and such.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
nbody_CPU_AltiVec: unbreak building as C code

Signed-off-by: Steven Noonan <steven@uplinklabs.net>