Add flag `-f(no-)object-code-if-unboxed`. Fixes #18955
Since MR !554 (merged) (#15454 (closed)) GHCi automatically enabled the flag -fobject-code
on
any module using the UnboxedTuples or UnboxedSum extensions.
MR !1553 (closed) (#16876 (closed)) allowed to inhibit the automatic compiling to object-code
of these modules by setting the fbyte-code
flag. However, it assigned 2
different semantics to this flag and introduced the regression described in
issue #18955 (closed).
This MR fixes this regression by introducing the flag
-f(no-)object-code-if-unboxed
to inhibit the automatic compilation to
object code for modules using the UnboxedTuples or UnboxedSum extensions.