CXXFLAGS: add -fcheck-new whenever -fno-exceptions is used

This is to avoid GCC to optimize null-pointer checks away, in case the
default operator new is used together with -fno-exceptions.

XorShift128:  Add some protection to handle the case where this logic could be called from the interrupt level.

sched/sched_cpuload_oneshot:  Use the oneshot timer with optional entropy to measuer cPU load if so configured.

Add missing eth support in stm32butterfly2/nshnet config

Fix compilation warnings for stm32 eth with certain configs

Fix wrong config for stm32butterfly2/nshusbhost

add stm32butterfly2 development board

Change stm32 adc dma callback to send channel number instead of index