swift234

Implement the rest of rdar://16242700

Fix a phase ordering problem: SILGen of a noreturn function doesn't drop an unreachable after the function,
and doing so is problematic for various reasons (all expressions would have to handle their insertion point
vaporizing, and would have to emit unreachable code diagnostics).  Instead, run a simple pass that folds
noreturn calls and diagnoses unreachable code, and do it before DI.  This prevents DI from seeing false
paths, and rejecting what seems like invalid code.



Swift SVN r14711