Some updates:

- Respond to Doug's code review feedback
   - Stop hacking around with scopes and use "emplace" to work around RAII in the inactive config case
   - Limit use of StringRef on the front-end, in favor of std::string
   - Use ArrayRef rather than SmallVector within IfConfigDecl
   - Reorder new property declarations on BraceStmt to prevent unnecessary alignment issues
- Update ParseBraceItems to better capture top-level declarations, rather than using token lookahead

Swift SVN r14306

lib/Frontend/Frontend.cpp

@@ -328,7 +328,7 @@ void CompilerInstance::performParse() {
         if (PrimaryBufferID == NO_SUCH_BUFFER ||
             (SF->getBufferID().hasValue() &&
              SF->getBufferID().getValue() == PrimaryBufferID))
-          performTypeChecking(*SF, PersistentState.getTopLevelContext(), 0);
+          performTypeChecking(*SF, PersistentState.getTopLevelContext());
 
     // If there were no source files, we should still record known protocols.
     if (Context->getStdlibModule())