swift234

remove the hasFixedLifetime bit from ValueDecl, now that AST-level 
capture analysis is gone.  This functionality is subsumed by SIL passes,
which turn boxes into stack allocations.

One minor detail of this is that dealloc_ref isn't implemented yet in IRGen
(rdar://14648382) and SILGen produces it for destructors (e.g. see 
test/SILGen/lifetime.swift).  To unblock progress, I just removed the 
llvm_unreachable in IRGen.


Swift SVN r6890