Hello,

In file variant.cpp, two handlers are defined

void SERCOM0_Handler(){  Serial1.IrqHandler();}
void SERCOM5_Handler(){  Serial.IrqHandler();}

I understand it simplify the life of many, e.g. but in my case, I use SERCOM5 as an SPI device and I have to comment out that ISR definition.

What I propose is to make this optional by adding define condition

#if !defined(_VARIANT_ARDUINO_ZERO_DISABLE_SERCOM_HANDLERS_)
void SERCOM0_Handler(){  Serial1.IrqHandler();}
void SERCOM5_Handler(){  Serial.IrqHandler();}
#endif

if it make sense, I will send a PR