* Fix multi-threaded IRGen: store the DeclContext in a SILFunction explicitly instead of deriving it from the debug location. It's used in IRGen to decide into which module a function is emitted. With -gsil the debug location is changed and that should not change the module decision.
* Erase debug_value/debug_value_addr instructions when using -gsil. Those instructions are not needed anymore. They can also trigger a verifier error.
