In case using an own pins_arduino.h for the ATtiny861 the compile stops in Tone.cpp.

This can be avoided adding an additional "#if defined" statement which catches the case of undefined WGM01:

Tone.cpp line 154:

if defined(TCCR0A) && defined(TCCR0B)

->

if defined(TCCR0A) && defined(TCCR0B) && defined(WGM01)