Its like attiny45 is using the 28 Pins "arduino_pin.h" file.. because when I delete "the arduino_pins.h" from "hardware\arduino\cores\arduino" folder. it works.
You should not be in the "real Arduino" path. Your boards.text and any core files should be in the user path...
\Users\you\documents\Arduino\hardware\MyArduBoard\board\core....
Using the above, you can have many different board.txt each with their own pin mappings and core files.
Ray