Handling of ASCII encodings introduced in D898 breaks Unicode terminal detection

D898 was primarily intended to fix hangs in the event that iconv was unavailable (namely #10298 (closed) and #7695 (closed)). In addition to this fix, it also introduced self-contained handling of ANSI terminals to allow compiled executables to run in minimal environments lacking iconv.

However, the behavior that the patch introduced is highly suspicious. Specifically, it gives the user a UTF-8 encoding even if they requested ASCII.

This has the potential to break quite a lot of code. At very least it breaks GHC's Unicode terminal detection logic, which attempts to catch an invalid character when encoding a pair of smart-quotes. Of course, this exception will never be thrown if a UTF-8 encoder is used.