Add -D__PROG_TYPES_COMPAT__ to build option1

Hello Adafruit!

First of all, thank you for the OONTZ, I just got it working as a midi devices and it's great!

However, I had to make the following change to the board.txt file in order to build the examples. GCC (4.9) would complain that `prog_uint8_t` is not defined. I thought I'd contribute this back!

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On newer versions of GCC, `prog_uint8_t` is marked as deprecated so we need to
define `__PROG_TYPES_COMPAT__` to be able to use it.