swift234

[sil-combine] Make cast optimiser less fragile

- The cast optimiser was asserting if it could not find the _forceBridgeFromObjectiveC implementations in the Foundation module (where all stdlib bridged types reside). Now it checks the module being compiled as well.
- If a bridging function cannot be found, don't assert and bail out instead. After all, it is just an optimization and even if it cannot be applied, we should not crash.

This makes Swift :: 1_stdlib/ArrayBridge.swift compile with -O.

rdar://20845536

Swift SVN r28295