How to define IRQ handler in CPP files

With MCUXpresso SDK, users could define their own IRQ handler in application level to override the default IRQ handler. For example, to override the default PIT_IRQHandler define in startup_DEVICE.s, application code like app.c can be implement like:

// c
void PIT_IRQHandler(void)
{
    // Your code
}

When application file is CPP file, like app.cpp, then extern "C" should be used to ensure the function prototype alignment.

// cpp
extern "C" {
    void PIT_IRQHandler(void);
}
void PIT_IRQHandler(void)
{
    // Your code
}