Simplify handling of the interactive package; fixes Trac #8831
This patch is really a fix to the big commint 73c08ab1 Re-work the naming story for the GHCi prompt (Trac #8649) which introduced the 'interactive' package See Note [The interactive package] in HscTypes The original commit set both (a) The tcg_mod field of TcGblEnv to 'interactive:Ghci4' (say) (b) The thisPackage field of DynFlags to 'interactive' But the second step interacts badly with linking. :loaded modules are in the package set by 'thisPackage' (usually 'main'); if you change that, then we try to link package 'main', but can't find it, and that is what happened in #8831. The fix was simple: do (a) but not (b). I changed Note [The interactive package] in HscTypes to describe this.