[interface-gen] Support passing Swift compiler arguments for header file interface generation

Resolves rdar://problem/33249361.

tools/SourceKit/lib/SwiftLang/SwiftLangSupport.h

@@ -358,6 +358,7 @@ public:
                                  StringRef Name,
                                  StringRef HeaderName,
                                  ArrayRef<const char *> Args,
+                                 bool AreSwiftArgs,
                                  bool SynthesizedExtensions,
                                  Optional<unsigned> swiftVersion) override;