Update to avr-libc 2.2.1

[jeremyherbert]

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Fixes https://github.com/osx-cross/homebrew-avr/issues/339

[jeremyherbert]

@ladislas this seems to be failing in a part that I didn't change?

[ladislas]

you must make a PR for each formula that you are modifying.

as we are compiling gcc from source each time, it will take too much time to have all the formulae in the same PR and if the last formula fails, the whole PR fails.

regarding the fail here, I'm going to fix this in a separate PR

[ladislas]

style has been fixed in #341

[retsplines]

Can we get this merged? ATtiny214 came out in 2017 and still isn't supported on macOS with brew install avr-gcc...

[jeremyherbert]

Sorry, I am planning on getting back to this soon but I am really low on time at the moment.