RakuAST: Fix reporting of unknown routines

The AST cannot supply the line number yet and giving that as 'unknown'
broke reporting of exceptions. Use -1 as a marker instead so the user at
least gets a name and a message.

src/Raku/ast/scoping.rakumod

@@ -623,7 +623,7 @@ class RakuAST::UndeclaredSymbolDescription::Routine
   is RakuAST::UndeclaredSymbolDescription
 {
     method IMPL-REPORT(RakuAST::Lookup $node, Mu $types, Mu $routines, Mu $other) {
-        nqp::bindkey($routines, self.name, ['unknown']);
+        nqp::bindkey($routines, self.name, [-1]);
     }
 }