Add support for desugared bool in EmitCore

[mbenke]

$ cat test/examples/boolbug.solc
contract Bug {
  function main() {
    return false;
  }
}

$ esolc test/examples/boolbug.solc 
test/examples/boolbug.solc
Emitting core for contract Bug

ERROR: translateTCon: unknown type sum
sum
in: function signature function main () -> sum((), ())
in: function main

sol-core: Emit core failed
CallStack (from HasCallStack):
  error, called at src/Solcore/Desugarer/EmitCore.hs:41:3 in sol-core-0.0.0.0-inplace:Solcore.Desugarer.EmitCore
  errorsEM, called at src/Solcore/Desugarer/EmitCore.hs:181:20 in sol-core-0.0.0.0-inplace:Solcore.Desugarer.EmitCore