AVR toolchain requirement added for Makefile.
AVR toolchain requirement added for Makefile.


Former-commit-id: 387677c3877fcd154d99902ecb315ef777e718eb
ricklon/chipKIT32-MAX,adamwolf/chipKIT32-MAX,tintin304/chipKIT32-MAX,tintin304/chipKIT32-MAX,tintin304/chipKIT32-MAX,chipKIT32/chipKIT32-MAX,tintin304/chipKIT32-MAX,majenkotech/chipKIT32-MAX,ricklon/chipKIT32-MAX,ricklon/chipKIT32-MAX,majenkotech/chipKIT32-MAX,EmbeddedMan/chipKIT32-MAX,adamwolf/chipKIT32-MAX,majenkotech/chipKIT32-MAX,majenkotech/chipKIT32-MAX,majenkotech/chipKIT32-MAX,tintin304/chipKIT32-MAX,ricklon/chipKIT32-MAX,tintin304/chipKIT32-MAX,chipKIT32/chipKIT32-MAX,tintin304/chipKIT32-MAX,majenkotech/chipKIT32-MAX,majenkotech/chipKIT32-MAX,EmbeddedMan/chipKIT32-MAX,adamwolf/chipKIT32-MAX,EmbeddedMan/chipKIT32-MAX,chipKIT32/chipKIT32-MAX,adamwolf/chipKIT32-MAX,EmbeddedMan/chipKIT32-MAX,EmbeddedMan/chipKIT32-MAX,EmbeddedMan/chipKIT32-MAX,adamwolf/chipKIT32-MAX,adamwolf/chipKIT32-MAX,adamwolf/chipKIT32-MAX,chipKIT32/chipKIT32-MAX,chipKIT32/chipKIT32-MAX,EmbeddedMan/chipKIT32-MAX,ricklon/chipKIT32-MAX,ricklon/chipKIT32-MAX,ricklon/chipKIT32-MAX,chipKIT32/chipKIT32-MAX,chipKIT32/chipKIT32-MAX