bug#74557: Bootstrap no longer working

[Mikael Djurfeldt]

After the latest improvements of psyntax, bootstrap is no longer working.
It yields:

  BOOTSTRAP(stage0) GUILEC ice-9/eval.go
Pre-boot error; key: unbound-variable, args: (#f "Unbound variable: ~S"
(error)

(Tested somewhere after commit c51fcfff)