swift234

SILGen: Implement thunking for C function pointer conversions.

If we have a C function pointer conversion, generate a thunk using the same logic we use for ObjC method thunks, and emit a pointer to that thunk as the C function pointer value. (This works for nongeneric, nonmember functions; generics will additionally need to apply generic parameters within the thunks. Static functions would need to gather the metatype as well.)

Swift SVN r25653