xcode_requirement: support linux

[iMichka]

2020-10-12T21:29:03.7866574Z [31mError:[0m undefined method `latest_version' for OS::Mac::Xcode:Module
2020-10-12T21:29:03.7867686Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/requirements/xcode_requirement.rb:33:in `message'
2020-10-12T21:29:03.7868902Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/tests/formulae.rb:199:in `map'
2020-10-12T21:29:03.7870227Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/tests/formulae.rb:199:in `satisfied_requirements?'
2020-10-12T21:29:03.7871547Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/tests/formulae.rb:593:in `formula!'
2020-10-12T21:29:03.7873156Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/tests/formulae.rb:20:in `block in run!'
2020-10-12T21:29:03.7875029Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/tests/formulae.rb:19:in `each'
2020-10-12T21:29:03.7876299Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/tests/formulae.rb:19:in `run!'
2020-10-12T21:29:03.7877495Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/test_runner.rb:119:in `run_tests'
2020-10-12T21:29:03.7878705Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/test_runner.rb:36:in `block in run!'
2020-10-12T21:29:03.7879908Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.3_2/lib/ruby/2.6.0/delegate.rb:83:in `each'
2020-10-12T21:29:03.7881136Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/portable-ruby/2.6.3_2/lib/ruby/2.6.0/delegate.rb:83:in `method_missing'
2020-10-12T21:29:03.7882519Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/test_runner.rb:25:in `run!'
2020-10-12T21:29:03.7883735Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/lib/test_bot.rb:126:in `run!'
2020-10-12T21:29:03.7884875Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Taps/homebrew/homebrew-test-bot/cmd/test-bot.rb:75:in `test_bot'
2020-10-12T21:29:03.7885882Z /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/brew.rb:119:in `<main>'

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[iMichka]

I agree to the comments above. I rewrote the PR to make the requirement a no-op on Linux. That's the most sensible solution.

[iMichka]

Should I move the mac-specific method content to the mac-only file too?

[MikeMcQuaid]

Should I move the mac-specific method content to the mac-only file too?

I don't think so, would be good to leave that as-is as Xcode itself is Mac specific.

I agree to the comments above. I rewrote the PR to make the requirement a no-op on Linux. That's the most sensible solution.

👍🏻

[iMichka]

This is ready for a new review then :)

[MikeMcQuaid]

Thanks @iMichka and sorry for all the back and forth here!