swift234

Don't allow the global search of imported modules to include the Builtin module,
wrapping up rdar://11187080

Now the only way you get access to the Builtin module is if you're the standard
library (currently modeled with the -parse-stdlib command line flag, will eventually
be part of build configuration goop or something).

This breaks a few of Jordan's serialization tests, which I've XFAILed after discussion.



Swift SVN r5777