Use simple nop codes for <= sse on x86-32.

The "CentaurHauls family 6 model 9 stepping 8" family of CPUs (flags:
fpu vme de pse tsc msr cx8 sep mtrr pge mov pat mmx fxsr sse up rng
rng_en ace ace_en) SIGILLs on long nop codes.