Turn on -fobject-code in GHCi when UnboxedSums in enabled
GHC 8.8.1 introduced a wonderful improvement to GHCi: automatically turning on -fobject-code when UnboxedTuples is enabled. However, UnboxedSums, which also requires -fobject-code, was overlooked. Fixing this is trivial and requires changing one or two lines of code.