Better error message when missing main

I was thinking we could have a better error message for Main modules without a main functions

We currently have:

(tmp) (^_^♪) touch B.hs
(tmp) (^_^♪) runhaskell B.hs

B.hs:0:53: error: [GHC-88464]
    Variable not in scope: main :: IO a0
    Suggested fix: Perhaps use ‘min’ (imported from Prelude)

It might be worth having an error message that highlights main being a special name for the entrypoint of the program (expected in Main module), with a special error code (that can further explain modules without module Name where are Main by default), instead of a generic "var out of scope error" which isn't clear in this context and even suggests using another prelude function min instead of main which is nonsensical.