Correct format:
```
//===--- Name of file - Description ----------------------------*- Lang -*-===//
```
Notes:
* Comment line should be exactly 80 chars.
* Padding: Pad with dashes after "Description" to reach 80 chars.
* "Name of file", "Description" and "Lang" are all optional.
* In case of missing "Lang": drop the "-*-" markers.
* In case of missing space: drop one, two or three dashes before "Name of file".
...unless the functions are declared [transparent], or if we're in an
immediate mode (in which case we won't get a separate chance to link
against the imported TUs).
This is an optimization that will matter more when we start dealing with
Xcode projects with many cross-file dependencies, especially if we have
some kind of implicit import of the other source files in the project.
In the future, we may want to parse more function bodies for the purpose
of inlining, not just the transparent ones, but we weren't taking
advantage of that now, so it's not a regression. (We're still not taking
advantage of it even for [transparent] functions.)
Swift SVN r7698
-Introduce PersistentParserState to represent state persistent among multiple parsing passes.
The advantage is that PersistentParserState is independent of a particular Parser or Lexer object.
-Use PersistentParserState to keep information about delayed function body parsing and eliminate parser-specific
state from the AST (ParserTokenRange).
-Introduce DelayedParsingCallbacks to abstract out of the parser the logic about which functions should be delayed
or skipped.
Many thanks to Dmitri for his valuable feedback!
Swift SVN r6580
