Add special case for :Main module in `GHC.IfaceToCore.mk_top_id`
See Note [Root-main Id]
The :Main
special binding is actually defined in the current module
(hence don't go looking for it externally) but the module name is rOOT_MAIN
rather than the current module so we need this special case.
There was already some similar logic in GHC.Rename.Env
for
External Core, but now the "External Core" is in interface files it
needs to be moved here instead.
Fixes #22405 (closed)