DUE missing sfr_defs.h AVR macros causes pre DUE code to break

There a are few macros in avr/sfr_defs.h that are not provided when using a
DUE board which can cause pre DUE code to break when used on DUE.
Those most notable macro is _BV()
But there are also a few others:
bit_is_set()
bit_is_clear()
loop_until_bit_is_set()
loop_until_bit_is_clear()

None of these macros are architecture specific and could
be used on any architecture.

My recommendation would be to create a sfr_defs.h down in the DUE avr
compatibility directory with appropriate versions of these macros.
And then include in Arduino.h