clang-modernize -use-nullptr

and s/\bNULL\b/nullptr/g for *.cpp/h/mm files not compiled on my machine

Source/DSPSpy/real_dsp.cpp

@@ -28,7 +28,7 @@ void RealDSP::Init()
 
 	u32 level;
 	_CPU_ISR_Disable(level);
-	IRQ_Request(IRQ_DSP_DSP, dsp_irq_handler, NULL);
+	IRQ_Request(IRQ_DSP_DSP, dsp_irq_handler, nullptr);
 	_CPU_ISR_Restore(level);
 }