[Sema] SR-2327: cherry-pick the change from pull request 4286 for swift-3.0-branch

[MnO2]

What's in this pull request?

This change is to cherry-pick the commit from master as requested in pull request 4286

**** The original description for change. ****
Improve the error message what SR-2327 has described.

With

do {
    guard 1 == 2 else { break }
}

prompt the more helpful error message of error: unlabeled 'break' is only allowed inside a loop or switch, a labeled break is required to exit an if or do

Resolved bug number: (SR-2327)

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…d' inside 'do' or 'if'

[tkremenek]

@swift-ci test macOS