swift

24fa9c87 - ClangImporter: Introduce the #ClangDeclarationImport diagnostic group.

ClangImporter: Introduce the #ClangDeclarationImport diagnostic group. The warnings that ClangImporter emits about issues it encounters while importing declarations from Clang modules should all belong to a diagnostic group so that users of `-warnings-as-errors` can control their behavior using the compiler flags introduce with SE-0443. It's especially important that these diagnostics be controllable since they are often caused by external dependencies and therefore the developer may not have any control over whether they are emitted. The `#ClangDeclarationImport` diagnostic group is intentionally broad so that developers have a way to control all of these diagnostics with a single `-Wwarning` flag. I fully expect that we'll introduce finer-grained diagnostic groups for some of these diagnostics in the future, but those groups should be hierarchically nested under `#ClangDeclarationImport`, which is supported by SE-0443. Resolves rdar://150524204.