swift234

Better handling of overflow diagnostics when user types are not available.

Currently, we use heuristics to determine if the conversion errors come from directly inlining the std integer types. However, if those operations are wrapped in another transparent function, we will not see the user-visible integer types anymore, so we fall back to Builtin types. Enhance the diagnostics in that case to specify if the sign-agnostic Builtin types are signed or unsigned.

This reverts r10484 and adds test cases.

Swift SVN r10512