The name of the pin is not important, the pin number is. The
oneWirePin definition is used for example
here. The code:
dataPort := dataPort and not(1 shl oneWirePin);
is interpreted by the compiler (after substitution of the macro definitions) as:
PORTB := PORTB and not(1 shl 0);
Note that in FPC 3.2.2 there are no named constants declared for pins (e.g. PB0 for pin 0 on portB). This is in my opinion unfortunate, since pin names are used in the hardware documentation.