swift234

IRGen: Emit an OBJC_CLASS symbol for @objc classes.

LLVM doesn't have interior symbols as a first-class concept, so generate module inline asm that defines the OBJC_CLASS symbol relative to the Swift metadata symbol. To prevent our system linkers from considering this symbol as the start of a new object and breaking apart class metadata objects, put the class metadata object into a no_dead_strip section.

This isn't quite enough to get the OBJC_CLASS symbol to be available--the symbol appears to show up in the .o as an undefined symbol and stripped out of the .dylib. John is investigating with the backend and linker teams as to why this is the case.

Swift SVN r14927