This just renames two `Errors.cpp` to different names to accomodate the
compaction of `libDemangling` into `swiftCoreRuntime`. This is important
as when statically linked we end up with two members with the same name
which produces a linker issue:
```
libswiftCore.lib(Errors.cpp.obj) : warning LNK4255: library contain multiple objects of the same name; linking object as if no debug info
```
