software_spec: add on_macos/on_linux to PourBottleCheck

[SeekingMeaning]

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Note: This PR is out-of-date, see #9439

Related to Homebrew/homebrew-core#66168

This PR allows pour_bottle? changes in linuxbrew-core to be migrated to homebrew-core

Before:

pour_bottle? do
  reason <<~EOS
    The bottle needs the Apple Command Line Tools to be installed.
      You can install them, if desired, with:
        xcode-select --install
  EOS
  satisfy { !OS.mac? || MacOS::CLT.installed? }
end

After:

pour_bottle? do
  on_macos do
    reason <<~EOS
      The bottle needs the Apple Command Line Tools to be installed.
        You can install them, if desired, with:
          xcode-select --install
    EOS
    satisfy { MacOS::CLT.installed? }
  end
end

[BrewTestBot]

Review period will end on 2020-12-07 at 19:17:47 UTC.

[BrewTestBot]

Review period ended.